CAIRO,  (DNA) – Egypt’s President Abdel Fattah al-Sisi has vowed to respond forcefully after attackers killed at least 235 worshippers in a packed mosque in restive North Sinai province, the country’s deadliest attack in recent memory.

Al-Sisi declared three days of mourning would begin Saturday, the day after the gun and bomb assault on the Rawda mosque, roughly 40 kilometres (25 miles) west of the North Sinai capital of El-Arish.

In a televised speech the president pledged to “respond with brutal force”, adding that “the army and police will avenge our martyrs and return security and stability with force in the coming short period”.

Several hours later Egyptian air force jets destroyed vehicles used in the attack and “terrorist” locations where weapons and ammunition were stocked, an army spokesman said.

Witnesses said assailants had surrounded the mosque with all-terrain vehicles and detonated a bomb. They then mowed down panicked worshippers as they tried to flee and used congregants’ vehicles they had set alight to block routes to the mosque.

The state prosecutor’s office said in a statement that 235 people were killed and 109 wounded in the attack, the scale of which is unprecedented in a four-year insurgency by extremist groups.