BEIRUT (AP) -- Twin blasts ripped through a university campus in Syria's largest city on Tuesday as students were taking exams, setting cars alight, blowing the walls off dormitory rooms and killing more than 80 people, according to anti-regime activists and a government official.

The opposition and the government blamed each other for the explosions inside Aleppo University, which marked a major escalation in the struggle for control of the hotly contested commercial hub.

Activists said forces loyal to President Bashar Assad launched two airstrikes on the area, while Syrian state media said a "terrorist group" -- the government's shorthand for rebels -- hit it with two rockets.

Either way, the explosions shattered the relative calm of the sprawling, tree-lined campus, signaling the creep of Syria's civil war into areas that were previously spared the violence that has killed more than 60,000 people and reduced entire neighborhoods to rubble.

The competing narratives about what caused the blasts highlighted the difficulty of confirming reports from inside Syria.

The Syrian government bars most media from working in the country, making independent confirmation of events difficult. Both anti-regime activists and the Syrian government sift the information they give to journalists to boost their cause. And civilians stuck in the middle avoid talking to the media, fearing reprisals from both sides for speaking their minds.

Aleppo has been the focus of a violent struggle for control since rebel forces, mostly from rural areas north of the city, pushed in and began clashing with government troops last summer.

The university is in the city's northwest, a sector still controlled by the government. Both activists and the Assad regime said those killed in Tuesday's blasts were mostly students taking their mid-year exams and civilians who sought refuge in the university dorms after fleeing violence elsewhere.

The blasts caused widespread destruction, scattering rubble and more than a dozen flaming cars across a wide street near a dormitory, according to videos shot on site. The dormitory's windows were blown out and some of its walls were gone, revealing beds and other furniture inside.

Students and rescue workers combed the rubble, carrying away the wounded.

Images circulated by activists showed dead bodies lying in the street. The photos and videos appeared to be genuine and corresponded to other Associated Press reporting.

Activists said a government warplane carried out two airstrikes on the university. To support their claim, they circulated a video they said showed a small trail of smoke left by a jet. They could not explain why the government would strike an area controlled by its forces.

"We have no idea why the plane hit there, but it was very clear that it was a plane that struck," said an Aleppo activist reached via Skype who spoke on condition of anonymity due to security concerns.

Syria's state news agency said a "terrorist group" -- government shorthand for rebels -- fired two rockets at the university from an area further north. It did not give numbers for the dead and wounded.

The scale of destruction appeared inconsistent with the rockets the rebels are known to possess.

Syria's U.N. Ambassador Bashar Ja'afari told a U.N. Security Council meeting on combatting terrorism that "a cowardly terrorist act targeted the students of Aleppo University as they sat for their mid-term examinations." He said 82 students were killed and152 were wounded.

The Britain-based Syrian Observatory for Human Rights cited students and medical officials as saying 83 people were killed, though it only had the names of eight of the dead. It said the death toll could rise because some of the 150 wounded were in critical condition.

The group, which relies on a network of contacts inside Syria, said it was unclear what caused the blasts.

Syria's crisis began with political protests in March 2011 and has since descended into civil war, with scores of rebel groups across the country fighting Assad's forces. The U.N. said this month that more than 60,000 people have been killed in the violence.

The explosions came a day after Syria's deputy foreign minister said Assad would not step down and was free to run in presidential elections scheduled for next year.

The statement was the most recent brushing off by Syrian officials of calls by Western countries that Assad step down and posed a new challenge to the United Nation's proposed peace plan.

Deputy Foreign Minister Faisal Mekdad said banning Assad from running would be against democracy.

"The president and many other candidates who may run will go to the people ... and be elected by the people," Mekdad said in English during an interview with the BBC. "The ballot box will be the place where the future of the leadership of Syria will be decided."

The international envoy tasked with Syria's crisis, Lakhdar Brahimi, has proposed a plan to end Syria's war with a cease-fire followed by the formation of a transitional government to run the country until new elections can be held.

Brahimi did not mention Assad by name, but said the transitional government would have "full executive powers" and would replace the Syrian leader.

Earlier this month, Assad dismissed calls that he step down and vowed to keep fighting.

The opposition says that Assad can play no role in a resolution to the conflict.

Syrian Prime Minister Wael al-Halqi arrived on Tuesday in Iran, Syria's strongest ally in the region, to discuss the country's crisis.

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Associated Press writers Bassem Mroue in Beirut, Albert Aji in Damascus, Syria, and Ali Akbar Dareini in Tehran, Iran, contributed to this report.