Ukraine crisis: Obama accuses Russia of flouting deal

US President Barack Obama has accused Russia of flouting a deal on Ukraine.

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 could impose further sanctions against Russia.

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.