Ukraine stepped up air patrols over Donetsk as a convoy of pro-Russian rebels moved through the city with an anti-aircraft gun in tow, threatening renewed violence after clashes left dozens dead.

Mayor Oleksandr Lukyanchenko urged residents of the central part of the city of 1 million people to stay indoors and away from their windows after shots were fired near the local headquarters of the State Security Service. The convoy of insurgents included two armored personnel carriers, the mayor’s spokesman, Maksym Rovinskyi, said by phone from Donetsk.

Troops killed “dozens” of separatists in an operation to reclaim the main airport in the self-proclaimed Donetsk People’s Republic, dealing the deadliest blow to the uprising to date, Interior Minister Arsen Avakov said yesterday. President-elect Petro Poroshenko has vowed to wipe out the rebels and re- establish order after winning office May 25. He must stabilize a shrinking economy and confront rebels who’ve captured swaths of the Donetsk and Luhansk regions.

“Russia’s goal was and is to keep Ukraine so instable that we accept everything that the Russians want,” Poroshenko said in an interview with German newspaper Bild that was published today. “I have no doubt that Putin can end the fighting with his direct influence.”

President Barack Obama called Poroshenko yesterday to congratulate him and offer “the full support of the United States as he seeks to unify and move his country forward,” the White House said in an e-mailed statement. They agreed to continue talking when Obama visits Europe next week, it said.

European Union leaders meeting in Brussels last night decided to put off further sanctions on Russia after Putin showed a willingness to work with Ukraine’s new leader and pulled back some troops from the Ukrainian border.

“The possibility of de-escalation is here, finally,” French President Francois Hollande told reporters after the summit ended. “But we still need this strict reminder.”

In their final statement, the leaders said the EU was working on “possible targeted measures” and agreed “to continue preparations” in case further steps are needed.

Russia is being asked to provide humanitarian aid to people in eastern Ukraine affected by the conflict and is seeking Ukraine’s help in allowing delivery of supplies, the Foreign Ministry in Moscow said on its website today. Russia expects “the fastest possible answer” from Ukraine, it said.

The Ukrainian government is pushing full-speed ahead with its operation to rid the country of insurgents, First Deputy Prime Minister Vitaliy Yarema told reporters in Kiev yesterday. “We’ll continue this operation until there are no terrorists on Ukraine’s territory.”

Ukrainian border guards stopped four trucks laden with ammunition from entering the country from Russia last night, Foreign Minister Andriy Deshchytsia said in an interview with Bloomberg TV today.

Deshchytsia also said authorities have located the four foreign election monitors who went missing late on May 26. The observers, from the Organization for Security and Cooperation in Europe, where abducted by “Russian Cossacks” and are being held in the Luhansk region, Deshchytsia said, declining to elaborate because talks to free them were continuing.

Ukraine has the “resources to deal with a local insurgency, and its security services are getting better organized,” Arkady Moshes, head of the EU’s Eastern Neighborhood and Russia program at the Finnish Institute of International Affairs, said by phone. “The elections showed that voters are tired of ongoing violence, giving the new president a mandate to act in a forceful way and end this.”

Ukrainian Eurobonds are set for the best monthly rally in four years. The yield on debt due April 2023 fell 23 basis points yesterday and strengthened again today, pushing the yield down to 8.76 percent at 3:30 p.m. in Kiev, the lowest level since April 4, data compiled by Bloomberg show. The hryvnia was little changed at 11.91 per dollar.

Poroshenko said two days ago that government forces won’t quit until separatists are completely defeated.

“They won’t last two or three months,” the president- elect said. “They’ll last a few hours.”

Putin, who has repeatedly denied aiding the insurgency, told Italian Prime Minister Matteo Renzi in a phone call yesterday that the military operation must stop.

Russia is reducing the number of soldiers stationed on its border with Ukraine to about 20,000 now from about 50,000, Interfax cited Ukraine’s border service as saying today. The Russian troops are leaving behind military infrastructure, suggesting they may return, according to Interfax.

Streets in Donetsk were virtually empty for a second day. Stores around the city were closed and stalls at the usually bustling Radio Rynok, a central market, were shuttered. Few drivers ventured out on Artema Street, the main avenue.

Separatists abandoned a road block on the highway between Donetsk and Krasnoarmiysk to the northwest. Troops blocked all major roads heading north of Donetsk to the rebel stronghold of Slovyansk, where fighting continued today.

“It’s extremely important for Kiev now to regain control over eastern cities like Donetsk, Mariupol and most importantly Slovyansk as soon as possible,” Volodymyr Fesenko, the head of the Penta Political Analysis Center in the Ukrainian capital, said by phone. “That’s why I expect the offensive by government troops in the east to intensify.”

The government will send a second battalion of the volunteer National Guard to join the operation in the east, Deputy Interior Minister Serhiy Yarovy said, Interfax reported.

The U.S. is monitoring the situation in eastern Ukraine and is “concerned” about the actions of the separatists, State Department spokeswoman Jen Psaki told reporters in Washington yesterday. She didn’t rule out the possibility of the Obama administration still applying industrywide sanctions.

“A mounting death toll in the conflict in eastern Ukraine may yet provoke a more forceful response from Russia,” Tatiana Orlova, a senior economist at Royal Bank of Scotland Group Plc in London, said in a research note. “The fighting also reduces the chances of President Putin recognizing Poroshenko as Ukraine’s legitimate president.”