Thick black smoke has been seen to be rising over the international airport in the eastern Ukrainian city of Donetsk as Kiev forces in control of the facility fight pro-Russian rebels attempting to seize it.

According to Reuters TV, the airport standoff, which escalated on Thursday, has been going on for months with sporadic shelling of nearby districts taking place.

In one such incident on Wednesday, at least 10 people, including parents and teachers, were killed after a school and a minibus were hit by shelling.

Children, arriving for the first day of school, were forced to shelter in the basement as the shelling yielded the highest single civilian toll since a ceasefire was struck between Kiev and pro-Russian fighters last month.

The pro-Kiev regional government of Donetsk based in the government-controlled city of Mariupol accused pro-Russian fighters from the "Donetsk People's Republic" of shelling the school.

Four adults were killed, it said in a statement. Six more died when another shell struck a minibus at a bus stop about 500 metres from the school.

'Moderating influence'

Official rebel website DNR Today blamed the attack on Ukrainian artillery, claiming rebels do not possess the relevant weaponry and saying two security guards at the school were among the victims.

Clashes have raged for days at several flashpoints around the region, with both sides blaming the other for violating the agreement that commits them to withdrawing weapons and establishing a buffer zone.

The United States has decried the violence while the European Union decided on Tuesday to keep Russian sanctions in place, maintaining pressure on Moscow in the worst East-West standoff since the Cold War.

German Chancellor Angela Merkel, during a telephone call with President Vladimir Putin, stressed Moscow's "responsibility" to act as a moderating influence over the pro-Russian fighters in Ukraine.

Source: Agencies