US President Barack Obama has warned President Vladimir Putin that Russia will face greater costs if it continues its “aggressive actions” in Ukraine.
Mr Obama urged his Russian counterpart to seize the opportunity of fresh talks to find a peaceful solution to the war that has raged since April last year. 
Mr Putin is due to meet with the leaders of France, Germany and Ukraine at a summit in Belarus on Wednesday.
However, there was intense fighting in eastern Ukraine ahead of the talks.
Correspondents say both sides are attempting to make territorial gains before any possible peace agreement.
At least one person was killed and several injured when a shell hit a bus station in rebel-controlled Donetsk early on Wednesday.
On Tuesday, four soldiers and at least eight civilians were killed in rocket attacks on a key military base and a residential area in Kramatorsk.
Government officials said the rockets were fired from a rebel-held area, but separatists denied being behind the attack.
More than 5,400 people have died since the conflict began and civilian casualties have risen in recent weeks.
Source: BBC News
