BEIRUT - A Syrian regime air strike hit a school in the main northern city of Aleppo on Sunday killing five children and four other civilians, a monitoring group said.

"Military aircraft struck a school in east Aleppo city and killed five children, three female teachers and one man," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights. He said a number of people were seriously wounded and the death toll was likely to rise.

Another child was killed in an air strike on a rebel-held neighbourhood of east Aleppo, the Britain-based Observatory reported.

The strikes come after a day after government forces and rebel fighters exchanged fire in the northern city, leaving at least 35 civilians dead. Many schools in Aleppo city have been forced to close, while others hold classes in basements.

Meanwhile, the head of the UN agency responsible for Palestinian refugees called from Damascus on Sunday for safe passage for people wishing to leave the Yarmouk camp on the city fringes that Islamic State insurgents are trying to take over.

UNRWA Commissioner General Pierre Krahenbuhl and another senior UN official are in the Syrian capital to find ways to ease the plight of some 18,000 people estimated to be trapped in Yarmouk, which has been under government siege since 2013.

A Syrian military source said the army was giving a chance for solutions aimed at resolving the situation in Yarmouk, which UN Secretary General Ban Ki-moon has said is "beginning to resemble a death camp".

Islamic State's arrival in Yarmouk has given the militant group a significant foothold a few kilometres (miles) from President Bashar al-Assad's seat of power.

Islamic State, which has already seized wide areas of eastern and northern Syria, has in recent weeks mounted several big attacks on regions closer to the main population centres of western Syria, both in government- and rebel-held areas.

Ban said last Thursday that residents of Yarmouk were being "held hostage" by Islamic State militants and other extremists.

He also said they "face a double-edged sword - armed elements inside the camp, and government forces outside".

Islamic State moved into Yarmouk last week. Aided by fighters from the al Qaeda-linked Nusra Front, it has seized large parts of the camp from other insurgents based there.

Krahenbuhl visited a Damascus school where he met several dozen evacuees from Yarmouk. "We are very concerned of course about the survival needs of the people inside Yarmouk," he said.

"We called for a very clear respect for the civilians who are inside Yarmouk, we called for the possibility for civilians to temporarily leave in a safe way Yarmouk, to be able to be assisted outside. We will continue to call for this.

"We are thinking very strongly of how we can provide some form of assistance to the people who are inside," he added.

The Syrian Observatory for Human Rights, a Britain-based group that monitors the four-year-old civil war via sources on the ground, has reported army air strikes on the camp since Islamic State moved in.

The military source told Reuters that was "absolutely not true", adding: "We are waiting, leaving the space for solutions that safeguard the situation of the civilians and their situation."

Ramzi Ezzedine Ramzi, deputy to the UN envoy to Syria, told Reuters on Saturday he left a meeting with Syrian Deputy Foreign Minister Faisal Mekdad on Saturday "quite satisfied and confident that there will be very good cooperation".