Russian President Vladimir Putin has said he is hoping for a peace agreement to be reached between Ukraine and pro-Russian rebels by Friday, reports GHN based on BBC.
Mr Putin urged both sides to stop military action in eastern Ukraine, adding that his views and those of his Ukrainian counterpart were very close.
Ukraine President Petro Poroshenko said they had agreed a "ceasefire process".
Meanwhile US President Barack Obama said Nato guaranteed the independence of its members the Baltic states.
"You've lost your independence once before, with Nato you'll never lose it again," Mr Obama said in the Estonian capital Tallinn.
He told his audience of US and Estonian military that their countries were stronger because they were democracies, but that their vision was threatened by "Russia's aggression against Ukraine".
"Nations have a right to determine their own future. This is why we stand with the people of Ukraine today," he said.
He added that Nato had to send an "unmistakeable message in support of Ukraine this week", as well as strengthening the defences of two other former Soviet republics, Georgia and Moldova.
A Nato summit opens in Wales on Thursday. It is expected to back plans for a rapid response force and bolster the alliance's presence in eastern Europe.