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.

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.

Ukraine and the West accuse Russia of sending troops and arms to support the rebels, but Russia denies this.

Rival agendas at Ukraine talks

Ukraine: Restore government authority over breakaway areas, though Donetsk and Luhansk regions could get greater self-rule; disarm rebel forces; withdrawal of Russian troops; restore Kiev's control over Ukraine-Russia border; full prisoner exchange.

Pro-Russian rebels: Separation from rest of Ukraine and recognition of "people's republics" of Donetsk and Luhansk; no disarmament of separatist forces; amnesty for separatist leaders.

Russia: Legal guarantees for rights of Russian-speakers in eastern Ukraine; full autonomy for Donetsk and Luhansk in a federal system - not necessarily independence; no return of Crimea to Ukraine; withdrawal of Ukrainian troops from combat zone.

EU and US: Restore Ukraine's territorial integrity; end Russian intervention in eastern Ukraine - withdrawal of all Russian troops and heavy weapons; effective monitoring of Russia-Ukraine border and demilitarised zone between the combatants; full democracy in Donetsk and Luhansk.

(BBC)