Syrian activists say government forces have raided college dorms and killed at least four people after an anti-government protest in Aleppo, as U.N. monitors renewed efforts to assess a frayed cease-fire.

Rights groups and activists said Thursday that forces used tear gas and live ammunition in the overnight raids at Aleppo University.

Activists say forces detained at least 200 students as they stormed the campus, following an opposition protest.

The French News Agency says forces also carried out at least two raids in Damascus province on Thursday.

The unrest has come a day after opposition groups said rebels killed 15 security force members during an ambush in Aleppo province.

Meanwhile, several dozen U.N. monitors are conducting visits in areas including the flashpoint Homs and Hama regions on Thursday.

The monitors are assessing the government and the opposition's compliance to a cease-fire and peace plan brokered by international envoy Kofi Annan.

The head of the mission, Major General Robert Mood, told reporters in Hama the observers' presence seems to have a “calming effect” in Syria.

On Wednesday, observers said the Syrian military still had heavy weapons stationed in some cities, and that the government and opposition had both violated terms of the peace plan.

The United Nations estimates at least 9,000 people have been killed since President Bashar al-Assad began cracking down on an uprising against him in March of last year.

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