(QHA) -

At least 13 people were killed and another 20 were injured, most of them seriously, as a result of shelling of a public transport stop in Donetsk on Jan. 22.

The cause of the explosion was not immediately clear, but some reports said a mortar or artillery shell hit a trolleybus.

This comes as Ukrainian military spokesman says government forces have withdrawn from terminal buildings at Donetsk airport, positions that they fiercely defended for months against pro-Russian separatists.

Meanwhile, foreign ministers of Russia and Ukraine agreed at the meeting in Berlin to move artillery back from the frontline.

A statement from the meeting, also attended by France and Germany’s foreign ministers, said the quartet had agreed artillery should be withdrawn in accordance with a ceasefire agreement signed in Minsk in September.

However, so far there has been little sign that a ceasefire can hold, and in recent days a new wave of heavy fighting has broken out, notably at the airport, a symbolic battlefield where Ukrainian forces appear to have sustained many casualties.