At least 13 people have been killed after a trolleybus was hit by shelling in the eastern Ukrainian city of Donetsk, according to reports from the city.
Ukraine's defence ministry blamed pro-Russian rebels, saying in a statement: "On Thursday, the terrorists shelled a trolleybus in Donetsk.
"The terrorists shelled the passenger transport from city residential areas controlled by the illegal militias."
But Moscow has blamed the attack on Ukrainian troops branding it as a "crime against humanity", aimed at undermining efforts to resolve the bloody conflict.
Following the deadly strike, separatists paraded around 20 captured Ukrainian soldiers through the streets of Donetsk as angry residents hurled pieces of glass and abuse at them.
Ukraine's defence ministry has said troops have withdrawn from the main area of the city's airport, where there has been intense fighting for several weeks.
BBC reports that the military still controls some parts of the airport, but six soldiers had died and another 16 were wounded.
The artillery attack in the rebel stronghold came as talks on the country's crisis led to an agreement to pull back heavy weaponry from a demarcation line defined in last year's Minsk agreement.
German Foreign Minister Frank-Walter Steinmeier brokered the deal with his counterparts from France, Russia and Ukraine during talks in Berlin.
"A lot depends on the question if that what we have agreed on will not only remain printed paper, but will also change the situation on the ground," Mr Steinmeier said.
In a joint statement released by the German foreign ministry, the ministers noted "with serious concern" that fighting in eastern Ukraine had severely escalated, causing the loss of many human lives.
"This must stop immediately and the regime of quiet must be restored," the statement said.
They called on signatories of the Minsk peace plan to meet in the coming days to implement the ceasefire and withdrawal of heavy weapons.
Conflict
Kiev and Moscow blame each other for failing to implement a ceasefire agreed in Minsk last September to end the conflict in eastern Ukraine, where more than 4,700 have died in fighting between the Ukrainian army and pro-Russian rebels.
The development comes after the Ukrainian President claimed more than 9,000 Russian soldiers are currently backing up pro-Moscow fighters in the separatist east of the country.
In a speech at the World Economic Forum in Davos, Petro Poroshenko said Russian troops were backed by a range of heavy weapons including tanks and artillery systems.
"We have more than 9,000 troops of the Russian Federation on my territory, including more than 500 tanks and heavy artillery and armed personnel carriers," he said.
"If this is not aggression, what is aggression?"
Russian Foreign Minister Sergei Lavrov challenged Kiev to "present the proof".
US officials later cranked up the diplomatic pressure on Russia with Secretary of State John Kerry calling Russia's actions "a blatant land grab".
More than one million people have been displaced since pro-Russian fighters seized eastern regions in Ukraine last Spring.
Originally posted at 8.36am
