Ukrainian President Petro Poroshenko has said that a "military threat from the east" cannot be ruled out even if a truce is reached between government troops and pro-Russian rebels in the east.
According to the BBC, Poroshenko's warning is widely seen as an indirect reference to Russia.
Russia is accused of backing the rebels by providing them with arms and soldiers.
Russian President Vladimir Putin has constantly denied the claims.
Earlier, Putin reportedly went on record to say that a war with neighbouring Ukraine would be "apocalyptic" but was "unlikely," a report said.
In his first comments since the ceasefire agreement took effect on February 12, Putin said that such an apocalyptic scenario was unlikely and added that he hoped "this will never happen," reported the CNN.
While asserting his support for the recent Minsk ceasefire deal, Putin stressed that it was the best way to stabilise eastern Ukraine. "Europe is just as interested in that as Russia," he said and added that nobody wanted a conflict on the edge of Europe.
He said that the Minsk deal had become an "international legal document" after the UN Security Council approved a Russian-drafted resolution endorsing it.