At least 28 people were killed in an airstrike on a Syrian refugee camp, activists said, as rebel forces, including jihadi militias, seized a strategic village near Aleppo from the regime. Women and children were reported among the victims of the bombardment on 5 May that hit the Sarmada camp in the northern Idlib province housing Syrians displaced by the conflict.

"The number of the dead is likely to rise," said Britain-based monitoring group The Syrian Observatory for Human Rights (SOHR), explaining that a large number of people suffered serious injuries.

Videos and photos from the camp showed desperate women and children with their faces covered in blood being loaded on a pick-up truck as rescuers walking among the charred bodies tried to put out flames devouring the camp's tents.

It was not immediately clear who carried out the airstrike, although fingers were pointed at the regime and its Russian backers because Sarmada lies within rebel-held territory.

The attack came as only 300km south-east, in Palmyra, a St Petersburg symphonic orchestra played a concert in the city's ancient ruins to celebrate the regime's victory over Islamic State (Isis) there.

The UN called for an independent investigation into the bombing that its humanitarian chief Stephen O'Brien said "could amount to a war crime."

British Foreign Secretary Philip Hammond described the incident as "horrifying". "This attack took place against the backdrop of a concert in Palmyra, a tasteless attempt to distract attention from the continued suffering of millions of Syrians," he said. "It shows that there are no depths to which the regime will not sink."

Meanwhile, fighting continued around Aleppo, despite the extension of a fragile truce between rebels and the government. SOHR and activists with opposition group the Local Co-ordination Committees confirmed that rebel forces and jihadists from al-Qaeda's affiliate Nusra Front conquered the village of Khan Touman 6km to the south of the contested city.

At least 30 government soldiers and 43 insurgents, including some suicide bombers, were killed in the battle, according to SOHR.

Russian orchestra Palmyra
A Russian orchestra from St Petersburg perform in the splendour of freed Palmyra\'s ruins Reuters