At least 20 dead in Syria after mortar attack

Mortar fire has hit an election rally in support of President Bashar al-Assad in southern Syria, killing at least 20 people, state media and activists say. The attack happened as Assad supporters gathered in a tent in the city of Deraa on Thursday evening. President Assad was not at the event.
Background:
Syria crisis: Mortars 'kill 20' at pro-Assad rally in Deraa [BBC]
U.S. steps up scrutiny of American fighters in Syria [Reuters]