A day-old ceasefire largely held along the bloodied frontline in eastern Ukraine on Wednesday but hopes of peace talks and pulling back heavy weaponry still hung in the balance. 

Residents in the main rebel stronghold of Donetsk experienced an unfamiliar silence overnight as both Ukrainian and rebel forces called off shelling.

The last Soviet leader Mikhail Gorbachev on Tuesday urged the United States and the European Union to "defrost" relations with Moscow despite tensions over Ukraine.

The 83-year-old said in an article published in state daily Rossiiskaya Gazeta that the Ukraine crisis had led the West not only to impose sanctions on Russia but also to wind up cooperation on global issues from counter-terrorism to climate change and disease epidemics.

The city of Kharkiv in Ukraine's industrial east has stayed out of rebel hands but a mysterious spate of bombings have triggered fears that Russia is trying to destabilize this key defense hub. 

Barely a week goes by without another bombing reported against Ukrainian military targets in the city of 1.4 million that once served as Ukraine's capital. 

Energy-starved Ukraine said on Tuesday it had received the first Russian natural gas shipments since a politically charged price dispute saw Moscow cut off supplies to its Westward-leaning neighbor in June.

The announcement means that the war-torn nation of 45 million people should have enough power to heat homes through the bitter winter months.

Ukrainian President Petro Poroshenko said Tuesday a ceasefire along the front line in the east of his country appeared to be holding after Kiev declared a "day of silence" in its war with pro-Russian separatists.

"Today, one and a half hour ago, we declared a new ceasefire," Poroshenko said at a public lecture in Singapore.

Ukraine and pro-Russian insurgents on Tuesday were preparing to put to the test a comprehensive ceasefire aimed at calming an upsurge of violence that has eroded trust between Moscow and the West.

Uncertainty swirled around the deal in the early morning hours on what the government has dubbed "a day of silence." 

The U.N. appealed Monday for $16.4 billion (13.4 billion euros) to provide aid to nearly 60 million people worldwide next year, with almost half the amount aimed at helping victims of Syria's drawn-out conflict.

"The rising scale of need is outpacing our capacity to respond," warned United Nations humanitarian chief Valerie Amos, stressing that 2014 has been marked by a sharp rise in the number of people affected by violent conflicts.

Ukraine and pro-Russian insurgents prepared Monday for their first comprehensive truce talks in three months aimed at calming an upsurge of violence that has further eroded trust between Moscow and the West.

Local authorities have reported the death of at least 11 civilians over a bloody weekend in which government forces and organised militias exchanged volleys of Grad rocket fire across the devastated industrial east.

Five civilians have been killed in fresh violence in eastern Ukraine, where more explosions and gunfire rang out on Sunday, two days before the start of a planned truce, officials said.

Three civilians were killed and 10 were wounded overnight in the rebel bastion of Donetsk, where further explosions and gunfire were heard Sunday morning, local authorities said.

French President Francois Hollande on Saturday became the first European leader to travel to Russia in an attempt to defuse the standoff with Vladimir Putin over Ukraine, as Kiev announced a fresh round of peace talks next week.

Hollande's meeting with Putin in the diplomatic terminal of an airport outside the capital came as the conflict in eastern Ukraine has plunged relations between the West and Moscow to a post-Cold War low.