Islamist militants linked to al Qaeda entered Idlib in northern Syria on Monday and opened up a new front in a city that has been controlled by President Bashar al-Assad’s forces for more than a year, both sides said.

State television said the Nusra Front militants infiltrated Idlib at dawn and were confronted by troops and pro-government militias. The Nusra Front said its fighters killed dozens, including officers, in the attack and seized buildings.

In 2012, other rebel groups, including the Western-backed Free Syrian Army, briefly took control of parts of Idlib but were pushed out by the army. […]