CAIRO, Jul 26 (Aswat Masriya) - A woman was killed and two children were injured when their house in North Sinai was hit by a shell from an unknown source on Sunday, medical sources said.

The shell struck the house after clashes between security forces and militants, an eyewitness told Aswat Masriya.  

Military sources said heavy clashes took place between security forces and militants belonging to Islamic State-affiliated group Ansar Bayt al-Maqdis, involving "heavy and medium weapons." 

They added in statements to Aswat Masriya that militants tried to attack security sites but security personnel prevented the attacks and "forced them to flee."

Although the majority of casualties from militant attacks in Egypt are security personnel, civilians have also been affected, many in similar rocket attacks on houses in North Sinai. 

On July 4, six civilians were killed in three attacks in different parts of North Sinai. 

Militancy has surged since July 2013, with the northern part of the peninsula being the site of most attacks. 

Earlier on Sunday, a bus carrying police personnel was bombed, injuring 18 conscripts. Ansar claimed responsibility for the attack. 

The North-Sinai based group, which changed its name to Sinai Province after pledging allegiance to Islamic State fighters last November, is increasingly claiming responsibility for attacks. 

It has claimed at least four attacks in July alone, including an attack on a naval vessel.