Pro-Russian rebels ready for a ceasefire in Ukraine

Pro-Russian separatists have said they were ready for a ceasefire with the Ukrainian government, arguing that it should be done “to prevent humanitarian disaster.”

The announcement comes after the government made increasing gains against rebel forces.

Alexander Zakharchenko, prime minister of the self-proclaimed Donetsk People's Republic, warned that Donetsk, the centre of rebel resistance, faced a lack of food, water, and electricity, but said the rebels were ready to defend the city of around one million people.

"In the event of a storm of the city the number of victims will increase by magnitude. We have no humanitarian corridors. There is no supply of medicines ... food supplies are nearing their end," he said.

Ukrainian officials say they are ready for a ceasefire but on condition the rebels surrender their arms.

Earlier, Kiev said it had headed off an attempt by Russia to send troops into Ukraine under the guise of peacekeepers with the aim of provoking a large-scale military conflict, a statement Moscow dismissed as a "fairy tale".

The White House said that during a call on Saturday, US President Barack Obama and German Chancellor Angela Merkel "agreed that any Russian intervention in Ukraine, even under purported 'humanitarian' auspices, without the formal, express consent and authorisation of the government of Ukraine is unacceptable, violates international law, and will provoke additional consequences."

Obama and British Prime Minister David Cameron also discussed the crisis and said tougher sanctions should be imposed on Russia if it sends troops into Ukraine, according to a statement from Cameron's office.