Egypt mourned as the death toll from a gun and bomb assault at a mosque rose to over 300, including children, in the deadliest attack the country has witnessed.

President Abdul Fattah Al-sisi Has vowed to respond with “the utmost force” after more than 300 people were killed at a North Sinai mosque during Friday prayers.

In a statement in Cairo Al-Sisi announced a period of mourning after the attack and said it would increase the country’s resolve to oppose terrorism.

The Al-Rawda mosque in the town of Bir al-Abed was bombed and fleeing worshippers were then gunned down.

The military has conducted air strikes on targets in nearby mountains.

No group has yet claimed the attack, the deadliest in recent memory.

Egyptian Security forces have for years been fighting insurgency in the Sinai Peninsula, and militants affiliated with so-called I.S. Have been behind scores of deadly attacks in the desert region.

They usually target security forces and Christian churches, and the bloody attack on a mosque associated with Sufi Muslims has shocked Egypt.