French President Francois Hollande and German Chancellor Angela Merkel are due to hold talks in Moscow to try to end escalating fighting in east Ukraine.
Their meeting with President Vladimir Putin follows urgent talks in Kiev, where a new peace plan was presented.
US Secretary of State John Kerry, who was also in Kiev, said the US wanted a diplomatic solution, but would not close its eyes to Russian aggression.
Moscow is accused of arming pro-Russian rebels - a claim it denies.
Russia also rejects claims by Ukraine and the West that its regular troops are fighting alongside the rebels against Ukrainian troops in the eastern Donetsk and Luhansk regions.
Clashes - which have intensified in recent weeks after a rebel offensive - have left nearly 5,400 people dead since April, the UN says.
As a result, a September ceasefire - signed in Minsk, Belarus - is now in tatters.
In separate developments on Friday:
• US Vice-President Joe Biden meets top EU officials in Brussels, as Washington considers sending weapons to Ukraine to fight the rebels;
• the annual security conference opens in Munich, with the Ukraine crisis likely to top the agenda
'Hopes for ceasefire'
President Hollande and Mrs Merkel will meet President Putin in Moscow later on Friday to discuss new peace proposals.
On Thursday, the two leaders examined the plan with Ukrainian President Petro Poroshenko, without releasing any details.
Mr Poroshenko said in a statement that the meeting with Ms Merkel and Mr Hollande "give hopes... for a ceasefire".
Ahead of the Kiev talks, Mr Hollande said he and Mrs Merkel would present a new peace proposal based on the "territorial integrity" of Ukraine, which could be "acceptable to all".
However, he warned that diplomacy "cannot go on indefinitely".
Meanwhile, Ukrainian Foreign Minister Pavlo Klimkin tweeted late on Thursday: "Good mtg of Normandy Troika. Minsk agts- roadmap to peace&territorial integrity of Ukraine. Specific steps 2 ensure implementation discussed."
And he added that Ukraine "is not being pressured", in an apparent reference to reports of possible concessions to Russia.
Meanwhile, reports in Russian media suggested that the plan envisages giving the rebel-held parts of the Donetsk and Luhansk regions a level of autonomy and agreeing a new ceasefire line reflecting rebel advances since September.
A spokesman for the Kremlin said Mr Putin would discuss "the fastest possible end to the civil war in south-eastern Ukraine", without elaborating.
The 12-point Minsk agreement includes calls for a ceasefire, the withdrawal of heavy weaponry from the "line of contact", a prisoner exchange and international monitoring of the Ukraine-Russia border.
The fact that Mrs Merkel has agreed to come to the Russian capital for the first time since this conflict began last year suggests she sees some hope of compromise, the BBC's Sarah Rainsford in Moscow reports.
Our correspondent adds that it is also a sign of European concern that if the US does start sending weapons to Kiev, it might provoke Moscow to increase support for the militants, rather than end it - in effect launching a dangerous proxy war at the heart of Europe.
'Reviewing options'
Speaking earlier on Thursday at a joint news conference with Mr Kerry, Ukrainian Prime Minister Arseniy Yatsenyuk said: "We need to get peace. But we will never consider anything that undermines territorial integrity... of Ukraine".
Mr Kerry accused Russia of violating Ukraine's sovereignty, saying that Russia had been acting with "impunity", crossing the Ukrainian border "at will with weapons [and] personnel".
"We are choosing a peaceful solution through diplomacy - but you cannot have a one-sided peace," Mr Kerry said.
He added that Mr Obama was still "reviewing all options", including the possibility of providing "defensive weapons" to Ukraine, due to the dangerous escalation in violence.
The US is currently only providing "non-lethal" assistance, like night-vision goggles and body armour.
Russian Foreign Ministry spokesman Alexander Lukashevich said any decision by the US to supply weapons to Ukraine would "inflict colossal damage to Russian-American relations".
Several senior Western officials have also expressed concern at the prospect of US arms being sent to Ukraine.
Some 1.2 million Ukrainians have fled their homes since last April, when the rebels seized a big swathe of the Luhansk and Donetsk regions following Russia's annexation of Crimea.
BBC
