BEIRUT (AP) -- Syrian activists say 52 people have been killed in twin explosions at the main university in the northern city of Aleppo.

The Britain-based Syrian Observatory for Human Rights said the number of dead was expected to rise because many of those injured in Tuesday's blast are in critical condition.

It says the dead included university students and civilians staying in the university dorms after being displaced by fighting between forces loyal to President Bashar Assad and rebels seeking to topple his regime.

It's unclear what caused the explosions, with each side blaming the other.