US President Barack Obama has said the international community cannot "stand idle" and allow Europe's borders to be redrawn with the barrel of a gun, as the conflict in Ukraine shows no sign of abating.

As he stood beside German Chancellor Angela Merkel at the White House following talks about the prospect of reviving a peace plan to end the conflict, Obama warned Russia that its isolation "will only worsen both politically and economically" if it continues on its current course.

Obama went on to stress that both the US and its European allies remain committed to finding a diplomatic solution to tensions with Russia over Ukraine, as he pledged to keep up economic sanctions on the nation.

Ukrainian soldiers ride on a self-propelled howitzer near Debaltseve, eastern Ukraine (Reuters)

Merkel said it was crucial that the West stand up for Ukraine.

"If we give up this principle of territorial integrity of countries, then we will not be able to maintain the peaceful order of Europe," she warned.

Their remarks come after Vladimir Putin warned Ukraine is on a “dead-end track fraught with a big catastrophe” if it continues with its military operations in the east of the country ahead of key peace talks later this week.

The Russian President showed no sign of backing down over the Ukraine crisis during an interview with Egyptian newspaper Al-Ahram before a summit with the leaders of France, Germany and Ukraine on Wednesday. He is to meet Merkel – dubbed chief mediator of the Ukraine crisis as the only Western politician with a stable working relationship with Putin – as well as France’s Francois Hollande and Ukrainian leader Petro Poroshenko.

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It is hoped that a peace deal will result from the meeting in the Belarussian capital Minsk.

Merkel has warned Obama against the provision of weapons by the West to Ukraine in a bid to calm the escalating violence.

Putin will not be spoken to in the language of ultimatums at talks on the Ukraine crisis, a Russian radio station quoted the Kremlin as saying.

In comments to Govorit Moskva radio, Kremlin spokesman Dmitry Peskov dismissed claims that Merkel has issued him an ultimatum.

“Nobody has ever talked to the president in the tone of an ultimatum - and could not do so even if they wanted to,” Peskov was quoted as saying.

Ukrainian troops launch a Grad rocket towards pro-Russian forces outside Debaltseve (Reuters)

Putin had said: “The most important condition for the stabilisation of the situation is immediate cease-fire and ending of the so-called ‘anti-terrorist’, but in fact punitive, operation in the south-east of Ukraine.”

“Kiev’s attempts to exert economic pressure on Donbas and disrupt its daily life only aggravate the situation. This is a dead-end track, fraught with a big catastrophe,” Putin added.

A total of 5,358 people have been killed and 12,235 have been wounded in the east Ukrainian regions of Donetsk and Luhansk as of last month.

A refugee carries a bag of food donated in aid at a volunteer centre in Slaviansk (Reuters)

Nearly a million people, including around 140,000 children, have also been displaced within Ukraine.

Putin also blamed the West for breaking promises to not expand Nato and, he claimed, making countries choose between them and Russia.

The West says Moscow is driving the rebels to fight Ukrainian troops by providing weapons, but this was denied by Russia who said that the insurgents are volunteers.

Ukrainian policemen and volunteers arrest suspected terrorists in Kiev (EPA)

In his interview, Putin reiterated Moscow’s line that the violence in east Ukraine was a reaction to a Western-supported “coup” in which protesters overthrew Viktor Yanukovich from the presidency in Kiev last February.

Yanukovich was ousted after he had refused to sign an association agreement with the European Union.