AMMAN, Jordan — Syria's main Western-backed opposition says 200 civilians are trapped in a mosque in a suburb of the Syrian capital as fighting rages outside between rebels and forces loyal to President Bashar Assad.

The Syrian Coalition called on the United Nations in a statement Sunday to send "a strong warning" to Assad that he "must immediately release" the civilians in the Damascus suburb of Qaboun.

It did not say if the 200 had sought refuge in the mosque or were already there praying when fighting began.

It warned that thousands of civilians in Qaboun could be "massacred" by Assad's army, as armored vehicles and elite forces move into the neighborhood.

The Britain-based Syrian Observatory for Human Rights said clashes in Qaboun that began after midnight had caused casualties.