Egypt mourned on Saturday as the death toll from a gun and bomb assault at a mosque in the Sinai Peninsula soared above 300, including children, in the deadliest attack the country has witnessed.

The Daesh group's Egypt branch is the main suspect in Friday's massacre, the latest attack in a long-running insurgency. It has yet to claim responsibility for the operation.

The army said warplanes had struck militant hideouts in North Sinai in retaliation.

According to the state prosecution, up to 30 militants in camouflage flying the Daesh group's black banner had surrounded the mosque and proceeded to massacre the faithful during Friday prayers.

Twenty-seven children were among the dead, it said. President Abdel Fattah El Sisi declared three days of mourning and vowed to "respond with brutal force" to the attack, among the deadliest in the world since the September 11, 2001, attacks on the United States.

"The army and police will avenge our martyrs and return security and stability with force in the coming short period," he said in a televised speech.

Hours later Egyptian air force jets pursued the "terrorists and discovered several vehicles used in the terrorist attack, killing those inside near the vicinity of the attack", an army spokesman said.

The state prosecutor's office said 305 people were killed and 128 wounded in the attack.

One of the wounded, Magdy Rizk, said assailants wore masks and military uniforms, and that extremists had previously threatened people in the area.

Relatives visited victims in hospital in the city of Ismailia near the Suez Canal where the wounded were taken for treatment.

Source: Khaleej Times