Angela Merkel and Francois Hollande are travelling to Kiev and Moscow with a new peace initiative, amid a flurry of diplomacy to end what has been described as "a war on Europe's edge".
The German Chancellor and French President's proposal is "based on the territorial integrity of Ukraine", and is in response to the deepening humanitarian crisis on the frontline of the conflict.
A spokesman for the Russian Foreign Ministry said Vladimir Putin was ready to hold constructive talks with the European leaders, and that Russia "will do everything it can" to help resolve the crisis in Ukraine.
However, he claimed the Ukrainian government was using weapons in the conflict zone which had effects similar to those of weapons of mass destruction.
There has been a considerable escalation of violence in recent days, and John Kerry is also in Kiev to meet the country's president, Petro Poroshenko.
As he arrived, the Secretary of State announced an additional $16.4m humanitarian aid to help civilians caught up in the conflict.
More than 5,000 people have been killed in the Ukraine conflict since last April, which flared up after Russia annexed Crimea.
The September Minsk peace plan called for tighter control of the joint Russia-Ukraine border, through which Kiev says Moscow is channelling fighters and equipment.
Much has changed on the ground, however, since September.
The separatists, who Kiev says are supported by Russian troops, have seized more than 500 sq km (193 sq miles) of territory.
Russia denies providing troops and support to help the separatists and supplying them with military equipment.
US and Western sanctions against Russia have led to the biggest crisis in Russia-West relations since the end of the Cold War more than 20 years ago. EU sanctions were expanded last week.
At the weekend, hopes of easing tensions were dashed with Ukraine’s representative and separatist envoys accusing the other of sabotaging negotiations.
The main members of the so-called contact group - Ukrainian former president Leonid Kuchma, a Russian diplomat and an Organization for Security and Cooperation in Europe official - had met at a state residence in the Belarussian capital Minsk, where they were joined by two separatist officials.
The talks were said to have broken up with no conclusion, with the atmosphere described as not fruitful.
