An air strike on a refugee camp in rebel-held northern Syria may have killed people by the dozens, as reported by monitors and witnesses.Images on social media showed tents destroyed at the Kamounia camp near Sarmada in Idlib province, close to the Turkish border. Some reports say the attack was by Syrian or Russian war planes but this has not been founded. The strike comes a day after the extension of a truce was confirmed. The Syrian military and non-jihadist rebel forces had agreed to a temporary truce around the the city of Aleppo, following pressure from the US and Russia. A nationwide cessation of hostilities has been in place since February, but it has come under severe pressure recently, particularly around Aleppo, where some 300 people have died in clashes over the past two weeks. The UN has warned that if the cessation fails, it would be "catastrophic" and could displace another 400,000 people. The Local Co-ordination Committees, an opposition activist network, said more than 30 people had been killed and dozens more wounded in the Sarmada attack. Images on its Facebook page showed the aftermath of fires among the blue tents in the camp, with the ground still smouldering. The fighting in Aleppo early this week has been the most intense there for more than a year so far. The Syrian Observatory for Human Rights monitoring group said that rebels had advanced into government-held western districts on Tuesday night but were pushed back by Wednesday morning. The Syrian military began observing a 48-hour truce in Aleppo from Thursday morning. The nationwide partial truce agreement does not include the so-called Islamic State nor the al-Qaeda-affiliated Nusra Front, however.