MOSCOW (AP) — The Latest on the poisoning of a Russian ex-spy in England (all times local):

4:15 p.m.

British Prime Minister Theresa May is visiting the city of Salisbury to see where former spy Sergei Skripal and his daughter were found unconscious after being exposed to a nerve agent.

May met members of the emergency services and health officials responding to the March 4 chemical attack.

May has blamed Russia, expelled 23 Russian diplomats and suspended high-level contacts with Moscow.

The British leader saw the bench where the Skripals were discovered — now one of several sites in the city cordoned off with police tape and a forensics tent.

Almost 200 troops trained in chemical weapons and decontamination are helping police with the investigation.

May said it was "great to meet some tourists" and see that people still coming in the picturesque cathedral city, 90 miles (145 kms) southwest of London.

4 p.m.

The leaders of the United States, France, Germany and Britain say they are united in blaming Russia for a nerve agent attack on former spy Sergei Skripal.

In a rare joint statement, President Donald Trump, President Emmanuel Macron, Chancellor Angela Merkel and Prime Minister Theresa May say "there is no plausible alternative explanation" to Russian responsibility in the March 4 attack in England.

They say Russia's failure to respond to Britain's "legitimate request" for an explanation "further underlines its responsibility."

The leaders say the use of a chemical weapon is "an assault on U.K. sovereignty" and "a breach of international law."

Britain has expelled 23 Russian diplomats and suspended high-level contacts with Moscow over the incident.

Russia is expected to take retaliatory measures soon.

3:50 p.m.

Russian President Vladimir Putin has chaired his security council to discuss tensions with Britain over the ex-spy's poisoning.

Putin's spokesman Dmitry Peskov said, according to Russian news agencies, that the participants in the meeting "expressed a great concern about the destructive and provocative position taken by the British side."

The meeting involved top Russian Cabinet members, parliamentary leaders and intelligence chiefs.

Britain has blamed Russia for the poisoning of former spy Sergei Skripal and his daughter and responded by announcing the expulsion of 23 Russian diplomats, the severing of high-level contacts with Moscow and other measures. Moscow has rejected the accusations and said it would retaliate, but hasn't yet announced its response.

3:30 p.m.

Russian Foreign Minister Sergey Lavrov says that Britain's refusal to produce proof of Russian involvement in the ex-spy's poisoning indicates its absence.

Lavrov said Thursday that Britain apparently hopes to cover up the absence of facts by "fanning anti-Russian rhetoric bordering on hysteria" in an attempt to rally support from its allies.

He charged that while Russia "had no motive" to poison ex-spy Sergei Skripal, its foes were seeking to use the incident to try to derail the soccer World Cup hosted by Russia this summer. He also charged that the "provocation with Skripal" helps British Cabinet distract public attention from its failure to win favorable conditions during talks on leaving the European Union.

Lavrov said Moscow expects London to abide by procedures of the international chemical weapons watchdog to investigate.

3:30 p.m.

NATO's chief says Britain has not requested any explicit help in the wake of the poisoning of a former Russian spy and he sees no need to activate the alliance's collective defense clause.

Secretary-General Jens Stoltenberg told reporters Thursday that it is important to respond to the nerve-agent attack, blamed on Russia, "in a measured way."

NATO's Article 5 is an all-for-one, one-for-all, clause which rallies all nations in the 29-member alliance to the aid of an ally under attack. It has only ever been used once, by the U.S. after the Sept. 11, 2001, attacks.

Stoltenberg said that Britain has not asked for Article 5 to be activated over the poisoning of Sergei Skripal and his daughter in England on March 4.

3:25 p.m.

NATO's chief says the use of a nerve agent on a former Russian spy is a threat to international security and allies have offered "practical support" to Britain if it requests help.

Secretary-General Jens Stoltenberg said Thursday that the poisoning of Sergei Skripal and his daughter in England on March 4, blamed on Russia, "is unacceptable. It has no place in a civilized world."

Stoltenberg told reporters that the attack is "a blatant and serious violation of norms and rules that are important for the security of all of us."

He said the attack seems to be part of a "reckless pattern of Russian behavior over many years."

Stoltenberg said he will discuss the attack next week with British Foreign Secretary Boris Johnson.

3:20 p.m.

Britain's defense minister says the U.K. is building a new chemical weapons research facility to help counter a growing threat from Russia and other states.

Defense Secretary Gavin Williamson said in a speech Thursday that Britain had been "naive" about the threat posed by states including China, Iran, North Korea and Russia.

He said the 48 million-pound ($67 million) Chemical Weapons Defense Center will help "ensure we maintain our cutting edge in chemical analysis and defense."

Thousands of frontline British troops will also be vaccinated against anthrax, in light of a growing chemical, biological, radiological and nuclear threat.

Williamson said the nerve agent attack on former spy Sergei Skripal is an example of how Russia is "ripping up the international rule book."

He said U.K.-Russia relations were "exceptionally chilly," and advised Russia to "go away and shut up."

2:25 p.m.

French President Emmanuel Macron says he will take measures in coming days in response to the poisoning of a former Russian spy in Britain.

Macron, speaking during a visit to central France Thursday, said British intelligence services shared with French services information that confirms Russia's involvement.

He told reporters "everything seems to indicate Russia's responsibility."

He said he will discuss the issue with German Chancellor Angela Merkel during a planned meeting in Paris Friday.

Macron did not say if he would maintain a visit to Russia scheduled for May.

2:05 p.m.

A Russian expert says the stockpiles of the Soviet-designed nerve agent that Britain said was used to poison an ex-spy have all been destroyed, with U.S. assistance.

Igor Nikulin said that the U.S. funded efforts to dismantle the stockpiles of the Novichok agent at a Soviet-era research facility in Uzbekistan in the late 1990s. The facility in Nukus was used by the Soviet Union in its chemical weapons program.

Nikulin, who has advised the United Nations in the past, said in remarks carried by the RIA Novosti news agency, that "the Americans also took some equipment for producing the gas to U.S. territory."

Russia declared in September that it completed the destruction of Soviet-era chemical weapons stockpiles, an effort that spanned decades.

1:40 p.m.

Russia's Foreign Minister Sergey Lavrov has warned that Moscow will soon respond in kind to Britain's decision to expel 23 Russian diplomats over the poisoning of a former Russian spy.

Lavrov, speaking in remarks carried by RIA Novosti news agency, said that Russia will "certainly" expel British diplomats. He said that the move would come "soon," but added Moscow would inform London via official channels before publicly announcing its countermeasures.

Lavrov said British accusations of Moscow's involvement in the poisoning of Sergei Skripal and his daughter are intended to distract public attention from Britain's troubled exit from the European Union.

He argued that "boorish and unfounded" accusations against Russia "reflect the hopeless situation the British government has found itself in when it can't meet the obligations given to the public in connection with exit from the EU."

12:55 p.m.

The Russian Foreign Ministry's spokeswoman says the accusations of Moscow's involvement in the poisoning of an ex-spy have been driven by domestic policy factors in Britain.

Maria Zakharova said Thursday British Prime Minister Theresa May apparently was "aiming to posture as a strong leader" by blaming Moscow for the poisoning of Sergei Skripal and his daughter.

Britain on Wednesday announced the expulsion of 23 Russian diplomats, the severing of high-level contacts with Moscow and other measures. Moscow said it would retaliate, but hasn't yet announced its response.

Zakharova said that Moscow expects Britain to produce evidence to back up its claims of Russian involvement, which she denounced as "unbelievable nonsense." She insisted that Russia has "no motive whatsoever" to poison Skripal and denounced U.S. support for the British claims as a reflection of "Russophobia."

12:40 p.m.

British Foreign Secretary Boris Johnson says Russia targeted a former spy with a military grade nerve agent to make it clear that those who defy the Russian state deserve to "choke on their own 30 pieces of silver."

Johnson told the BBC on Thursday there was a message in the "smug, sarcastic response" from Moscow after the attack on Sergei Skripal and his daughter. Johnson says the Russians "want simultaneously to deny it and yet at the same time to glory in it."

Johnson says "the reason they've chosen this nerve agent is to show that it's Russia, and to show people in their agencies who might think of defecting or of supporting another way of life, of believing in an alternative set of values, that Russia will take revenge."

12:30 p.m.

French President Emmanuel Macron has expressed his solidarity with Britain after the poisoning of an ex-spy.

The president's office says in a statement Thursday Macron shares Britain's views that there is "no other plausible explanation" than Russia being involved in the attack, following a phone call with British Prime Minister Theresa May.

Macron says Britain has kept France closely informed of the evidence gathered by British investigators and "elements proving Russia's responsibility in the attack".

Macron and May condemn the use of a chemical weapon, the statement said.

They agreed on the importance of European countries and NATO members' unity in the response to this issue.

11:50 a.m.

The head of Russian state-funded RT television says British Prime Minister Theresa May is to blame if British media are kicked out of Russia over the poisoning of an ex-spy.

RT editor-in-chief Margarita Simonyan dismissed accusations that Russia was behind the nerve agent attack on Sergei Skripal. It prompted threats to shut down RT's British operations, among other actions targeting Moscow.

Simonyan told The Associated Press in Moscow that "if we are censored in the U.K., that's going to be it for the British media" in Russia.

She said it would be strange for Russia to be so "reckless and stupid" as to poison Skripal "knowing what outrage it would cause."

Skripal and his daughter are in critical condition in a British hospital after an attack that brought Russian-British relations to a post-Cold War low.