German Chancellor Angela Merkel on Saturday pushed a new peace bid to end the Ukraine conflict, warning that sending weapons to government forces fighting pro-Russian rebels would not stop the bloodshed.

Fresh from overnight talks in Moscow with French President Francois Hollande to thrash out a new peace plan, Merkel said success was far from assured but it was essential to try.

The United States and Europe must stand together over Ukraine as it battles for survival in the face of escalating Russian military involvement, Vice President Joe Biden said during a visit to Brussels on Friday.

"We, the U.S. and Europe as a whole, have to stand with Ukraine at this moment," he said, amid reports of transatlantic divisions over whether to send weapons to support the Western-backed Kiev government.

Convoys of buses arrived in Ukraine's frontline town of Debaltseve on Friday to take besieged civilians to safety after both sides agreed a brief humanitarian truce, an Agence France Presse correspondent said.

Around 25 buses from both the Ukrainian and pro-Russian separatist sides drove into the shattered strategic town that has been the centre of fighting in recent days.

U.S. senators from both parties renewed calls Thursday for President Barack Obama to boost military aid to Ukraine, while criticizing Europe's approach to the crisis.

The Obama administration has been under fire for months from some lawmakers who have criticized its failure to move decisively to provide Ukraine with "defensive lethal assistance" to defend itself against rebels backed by Russia.

German Chancellor Angela Merkel and French President Francois Hollande flew to Kiev Thursday with a new peace plan, in the biggest diplomatic push yet to halt an upsurge in deadly fighting in eastern Ukraine.

The two European leaders, who will present the plan to Russia Friday, arrived hot on the heels of US Secretary of State John Kerry, who said that Moscow held the cards to end the conflict.

U.N. Secretary-General Ban Ki-moon on Wednesday joined calls for a temporary truce to allow civilians to be evacuated from the frontline town of Debaltseve in east Ukraine.

Ban said he was particularly concerned by the plight of civilians trapped in Debaltseve, a strategic railway hub linking two rebel-held cities.

U.S. Vice-President Joe Biden will huddle with leaders from Germany and Ukraine on an upcoming visit to Europe, as allies plot a response to increased violence in Ukraine.

Biden later this week will travel to Belgium and Germany, where he will attend a high-profile security conference in Munich.

France has no plans to supply weapons to Ukraine to tackle the pro-Russian insurgency in the east of the country, Defense Minister Jean-Yves Le Drian said Wednesday.

"We have no intention of supplying lethal weapons at this time," Le Drian said, responding to a mounting debate triggered by reports that the United States is considering arming the Ukrainian government.

Shelling at a hospital in east Ukraine killed four people on Wednesday ahead of a visit to Kiev by U.S. Secretary of State John Kerry that will see possible arms supplies high on the agenda.

The latest deaths came as international pressure grew for an immediate halt to surging violence which has seen hundreds of civilians killed in recent weeks as pro-Russian rebels pushed into government-held territory.

Ten people were killed in a head-on collision in Russia not far from the Ukraine border Wednesday when a minibus drove into a truck, police said.

The crash in the Belgorod region -- about 40 kilometers (25 miles) from the border of eastern Ukraine's Kharkiv region -- saw the minibus swerve into oncoming traffic and hit a large semi-trailer truck, police in the Belgorod region said in a statement.