Syrian doctors treat an injured man who was wounded at the open-air cafeteria at Damascus University on March 28, 2013. Mortar shells slammed into a cafeteria at Damascus University, killing at least 12 people and wounding scores, according to state media. (SANA/via AP)

Mortar rounds crashed into the campus of the University of Damascus on Thursday, killing at least a dozen people and wounding several others, according to official Syrian media and opposition groups.

State media blamed the attack on “terrorists,” their label for the opposition, and rebels attributed it to the government.

“Each time the Free Syrian Army attacks regime targets, the regime retaliates on residential areas to make it look like the Free Syrian Army is attacking civilians and universities,” said Loay Meqdad, a spokesman for the FSA, the Syrian opposition’s main military group. “The regime attacked the university.”

Fighting has spread across Damascus in recent months, following the launch of a rebel offensive to take control of the capital.

The mortar rounds fired Thursday struck a cafeteria area in the Architecture College in the early afternoon, when students were on campus. The attack recalled a double explosion at the University of Aleppo in January — thought to be caused by rockets or missiles — that left more than 80 dead. Government officials and rebel leaders also blamed each other for those deaths.

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Separately Thursday, rebels claimed to have shot down an Iranian plane carrying weapons and supplies for the Syrian military as it attempted to land at Damascus International Airport.

Rebels have often accused Iran of supporting the government of Syrian President Bashar al-Assad with men and materiel, an assertion that the Iranian government has denied.

Meqdad said rebel fighters planned the attack after receiving information about the plane’s arrival time and its cargo from an airport worker who is sympathetic to the opposition.

A shaky video posted online by a rebel group called the Daraa al-Islam brigade shows a large aircraft descending near a grove of trees and bursting into flames. As the plane veers away, a man off camera shouts: “It’s burning! It’s burning! Allah is making us happy.”

The plane crashed at the airport, destroying other aircraft and cargo, the rebel group said in a short statement posted with the video. Meqdad said the crash caused a large fire at the airport, as ammunition and weaponry aboard the plane exploded.

The state-run Syrian Arab News Agency denied reports of any irregularities at the airport and said flights were arriving and departing normally.

The University of Damascus has been running on a reduced schedule during the recent fighting, with most classes ending by 4 p.m. to allow students to get home before dark.

Photos posted on SANA’s Web site show a large hole in a tarp covering the cafeteria area and blood splattered across the floor and tables. Sunglasses, bloody notebooks and other personal items can be seen near overturned chairs.

Footage aired by the official al-Ikhbariya TV channel shows doctors frantically pumping the chest of one man and a body being covered and wheeled away by medical staff members.

Despite the rebels’ denial of responsibility for Thursday’s attack, opposition fighters, in recent weeks, have carried out mortar attacks close to the university campus, which is in central Damascus. In particular, they have targeted nearby Umayyad Square, where the headquarters of the military chiefs of staff and the offices of Syrian state television are located.

Still, activists say rebel fighters would not have carried out an attack at that time of day because of the high risk of hitting civilians.

“These attacks happened in the peak of the rush hour in the city where a large number of civilians would be present,” an activist in Damascus who goes by the name Salahaldin said in a Skype interview.

Suzan Haidamous and Ahmed Ramadan contributed to this report.