Syria braced for opposition protests on Friday as U.N. officials expressed concern that al-Qaida may have played a role in recent attacks that have further strained a fragile cease-fire.

Anti-government activists urged protesters to take to the streets under a slogan of “heroes” of Aleppo University, on Friday, in a show of support for students who were confronted by security forces during a Thursday protest.

Meanwhile, U.N. Secretary-General Ban Ki-moon said he believes al-Qaida is behind twin bombings in Damascus, last week, that killed 55 people.

He said Thursday the terror group's possible involvement had “created again very serious problems.” He also said Syria's death toll from 15 months of anti-government related unrest may have reached 10,000.

In a Friday news conference, the U.N. observer mission head, Major General Robert Mood, said an al-Qaida presence would be a “worrying development.”

“I'm concerned about the incidents where explosives, improvised devices, are targeting innocent civilians, innocent people, because it is not going to help the situation.”

Also Friday, opposition activists said there was intense government shelling in Rastan, an opposition stronghold in the Homs region. On Thursday, the Syrian Observatory for Human Rights said machine gun fire killed three people in the region.

The observatory and Syrian state-run media say assailants opened fire on a bus carrying law enforcement officers in Homs on Thursday, killing one person. The government blamed “armed terrorists” for the attack.

The United Nations says more than 9,000 people have been killed in violence related to the anti-government uprising that erupted more than a year ago.