MOSCOW - An Islamist group from Russia's restive Caucasus region has claimed responsibility for this week's deadly twin suicide bombings in Moscow, while two more attacks on Wednesday left 12 dead.

The leader of the Islamist "Emirate of the Caucasus" threatened more attacks while claiming the Moscow metro strikes by two female suicide bombers that killed 39, two Internet sites reported Wednesday, citing a video message.

Last month, Islamist rebels led by the same militant leader, Doku Umarov, who uses the nom de guerre Abu Usman, pledged a holy war, saying attacks would be staged throughout the country.

The claim of responsibility for the metro attacks was reported by the SITE monitoring group and a Chechen Internet site.

In the claim, the Islamist leader called the attacks revenge for a "massacre by Russian invaders of the poorest residents of Chechnya and Ingushetia" on February 11 when they were "picking wild garlic ... to feed their families."

The "war will come to your streets, and you will feel it with your own lives and skins," he warned in the first claim of responsibility for Monday's metro bombings, though its authenticity could not be independently confirmed.

Russian Prime Minister Vladimir Putin said the latest attacks, which occurred in the North Caucasus on Wednesday, may be linked to the bombings of the Moscow metro.

Russia has for years been fighting an Islamist-fuelled insurgency in the North Caucasus but the metro bombings in the heart of Moscow, largely spared attacks for the last six years, shook the country to its core.

Nine police including a local police chief were among the dead in the double attack 48 hours after the Moscow bombings in the North Caucasus region of Dagestan, a region on the Caspian Sea already wracked by militant violence.

"I do not rule out that the same gang (as in Moscow) was at work here," a stern-looking Putin told a government meeting in televised remarks.

President Dmitry Medvedev meanwhile told a security council meeting that "the terrorists' goal is the destabilisation of the situation in the country, the destruction of civil society, a desire to sow fear and panic among the population."

"We will not allow this," he added.

Wednesday's first blast was caused by a car occupied by a suicide bomber that blew up when police tried to stop it during a regular check in the town of Kizlyar in Dagestan, officials said.

The force of the first blast left a massive crater and reduced surrounding cars to burned-out wrecks.

After 20 minutes, another blast was caused by a second suicide bomber wearing a police uniform who approached police working at the scene of the first blast, a spokeswoman for the Dagestani interior ministry told AFP.

Investigators said the first blast was caused by explosives of 200 kilogrammes of TNT equivalent stuffed into a Niva jeep, Interfax reported.

The investigative committee of Russian prosecutors said in a statement that 12 people were killed, nine of them police, and 23 were wounded. Among the dead was local Kizlyar district police chief Vitaly Vedernikov.

Russia's leaders pledged after Monday's blasts to hunt down and destroy the organisers of the bombings who they said had links to North Caucasus militant groups.

Muslim Dagestan has been one of the Caucasus regions most troubled by violence, along with Chechnya and Ingushetia.

Security in the tense Russian capital was further intensified after the new attacks.

Moscow's police chief Vladimir Kolokoltsev said three times as many police as usual were on patrol in the metro system.

The head of the metro, Dmitry Gayev, said that as part of new security measures the metro would start to introduce chemical detectors at stations from April.

Putin had Tuesday ordered security forces to snare the masterminds of the metro bombings, saying they should be scraped out from the sewers in language reminiscent of a 1999 promise to strike at rebels in the "outhouse".

The Kommersant daily quoted an investigation source as saying Tuesday that militants had recruited 30 potential suicide bombers in recent months, with 21 still at large after nine already blew themselves up.

Police have also released grisly photographs of the two bombers' severed heads. Unconfirmed reports have said they arrived in Moscow from the Caucasus by bus early Monday.

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