A video showing protesters at Aleppo University taking shelter in a UN monitoring vehicle while Assad's security forces beat fellow students outside has emerged from demonstrations in the second largest city in Syria.

Opposition groups have dubbed the raid "Heroes of Aleppo University" to honour the four students who were killed earlier this month during clashes between the regime's militia and students.

On that occasion, Assad's forces and pro-regime thugs from the Shabiha militia stormed a student dormitory, firing tear gas and live ammunition to disperse the 1,500 students who resided there.

Angry activists reported on Twitter that some students were allegedly thrown off the roof by members of Assad's militia.

"Syrians are protesting today under the banner "Heroes of Aleppo University. The students definitely earned that title," read a tweet by Shakeeb Al-Jabri, Syrian revolutionary and Al-Ayyam English staff writer.

As a UN monitoring group visited the city, hundreds of students converged on the university, where they were set upon by pro-government students and security forces.

Meanwhile, Robert Mood, head of the UN's monitoring team, said without dialogue observers can do nothing to achieve peace.

There are currently 257 monitors deployed throughout the country.

UN Secretary-General Ban Ki-moon pointed out UN monitors have been attacked twice as fighting continues to rage.

"The deployment of monitors has some dampening effect, the number of violence has reduced but not enough, not all the violence has stopped," Ban said to a youth group visiting the UN headquarters in New York.

"We are trying out best efforts to protect the civilian population," he added.

In another dramatic development, Burhan Ghalioun, head of the Syrian National Council (SNC), announced he is resigning his position amid growing divisions within the umbrella opposition group.

"I will not allow myself to be the candidate of division, I am not attached to a position, so I announce that I will step down after a new candidate has been chosen, either by consensus or through new elections," he said in a statement.

His resignation came just hours after the Local Coordination Committees (LCC), a network of activists on the ground, threatened to pull out of the SNC. The LCC criticised leaders of the SNC for failing to closely collaborate with activists on the ground and wanting to "monopolise" power.

University students in Aleppo, which is Syria's business hub, have staged almost daily protests calling for Assad to step down.

Activists have renamed Aleppo University as the "University of the Revolution" to honour the students who have been killed in the conflict.