US President Barack Obama said on Thursday he was poised to impose new sanctions on Moscow if it does not act fast to end an armed stand-off in Ukraine, but there was a first, tentative sign that pro-Russian separatists were ceding ground.
Under an international accord signed in Geneva last week, illegal armed groups in Ukraine, including the pro-Russian rebels occupying about a dozen public buildings in the east of the country, are supposed to disarm and go home.
In what has become the worst stand-off between Russia and the West since the Cold War, Washington accuses Moscow of fomenting unrest in Ukraine's east. Russia denies that and counters that Europe and the United States are propping up an illegitimate government in Kiev.
"So far at least we have seen them not abide by the spirit or the letter of the agreement in Geneva," Obama said of Russia on a visit to Japan.
"We have prepared for the possibility of applying additional sanctions," he told a news conference. "There's always the possibility that Russia, tomorrow, or the next day, reverses its course and takes a different approach."
Russian news agencies quoted Foreign Minister Sergei Lavrov as saying that he expected "the Geneva accords will be implemented in practical actions in the near future".
In NATO member Poland, the first group of a contingent of around 600 U.S. soldiers arrived on Wednesday. They are part of an effort by Washington to reassure eastern European allies who are worried by a build-up of Russian forces near Ukraine's borders.
In Ukraine, the Western-backed government said the city hall in Mariupol, which had been seized by pro-Russian separatists, was now back under central control. Interior Minister Arsen Avakov said the mayor was back in his office, and that explosives experts were checking the building to make it safe.
"In this instance there were no casualties. And that is good and proper. The process of getting the situation back to normal in the city will continue," Avakov said in a post on his Facebook page.
Mariupol, an industrial city on the Azov Sea, was the scene of violent clashes last week when, according to the Kiev government, separatist attackers tried to storm a base of the Ukrainian national guard.
If the Mariupol city hall is indeed back under Kiev's control, it would be the first substantial sign that the Geneva accord is being implemented.
But Kiev also reported a shootout overnight in another part of the