Ukraine crisis: Tensions prompt military exercises

President Barack Obama has warned Russia that he is ready to impose more sanctions if it refuses to implement an agreement to reduce tensions in eastern Ukraine.

His comments came as the first contingent of US troops landed in Poland for military exercises. An initial 150 soldiers are to be followed by a further 450 within days.

Natalia Antelava, is in Ukraine's eastern city of Donetsk where many pro-Russian militants have been active.