A truce in the Syrian city of Aleppo has been extended for three days to "prevent the situation from worsening," the Russian defense ministry said, according to BBC News.

The Syrian army announced a two-day truce on Wednesday, May 4, after two weeks of clashes left nearly 300 civilians dead.

The truce is part of international efforts to build on a wide-ranging ceasefire introduced in February.

Russia has been supporting its allies in the Syrian government with air strikes since September 2015.

Aleppo, in north-west Syria, was the country's industrial and financial centre before the five-year civil war started. The recent violence there has been the worst phase of the war in the city for more than a year.

The nationwide cessation of hostilities brokered in late February by the U.S. and Russia, which back opposing sides in the war, is close to collapse, BBC says.

Russia said on Wednesday that it had withdrawn about 30 aircraft from its airbase in Syria, including all of the Su-25 ground attack planes stationed there.

The Russian military began the withdrawal of most of its forces from Syria in March, six months after launching an air campaign to bolster President Bashar al-Assad.

To the south of Aleppo, combat continues between the Syrian army and rebels including the al-Nusra Front, an al-Qaeda affiliate that is not included in the cessation of hostilities.