There were no reports of serious injuries during the overnight operation in the city, where three pro-Russian protesters were recently shot dead.But local media quote the self-proclaimed Donetsk People's Republic as saying it still controls the city hall.US President Barack Obama has accused Russia of flouting a deal on Ukraine.Pro-Russian separatists have taken over administrative buildings in at least a dozen towns in eastern Ukraine in a bid to seek closer ties to Moscow.Mr Obama told a news conference in Japan that Moscow had failed to halt actions by militants in the region and warned that the US had further sanctions against Russia "teed up".A contingent of US troops has begun landing in Poland for military exercises amid concerns among Nato's eastern members about Russian intentions.Moscow has said it will respond to any attack on its interests in Ukraine.Unrest began in Ukraine last November over whether the country should look towards Moscow or the West.ClashUkrainian Interior Minister Arsen Avakov announced on Thursday that the city hall in Mariupol, a port on the Sea of Azov, had been "liberated" overnight without any casualties."Civic activists" played a major part in the operation, he said.However, local news website 0629 reported that the self-proclaimed People's Republic of Donetsk was still claiming control over the mayor's hall after a struggle with attackers.Mr Avakov also reported that Ukrainian troops in Artemivsk had fended off an attempt by dozens of pro-Russian militants to seize weapons from a military unit. One soldier was wounded, he said.Unverified footage of military helicopters, said to be flying over Artemivsk, was posted by a blogger on YouTube.(BBC)ANN.Az