Retaliation for deadly attack on mosque.

Egypt has launched air strikes on suspected terrorist hideouts in the Sinai Peninsula after a terrorist attack on a crowded mosque claimed at least 235 lives. It was the most deadly attack yet by Isis extremists in Egypt.

The military won't rest until those involved in Friday's deadly attack have been eliminated, local state-run newspaper Al-Ahram quoted Egyptian security sources as saying. Several suspects had already been killed, the source added.

After the deadly attack, Egyptian President Abdel-Fattah al-Sisi vowed a "harsh" response to the massacre, which also injured 109.

"The armed forces and the police will avenge our martyrs and restore security and stability with the utmost force," al-Sisi said.

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"What is happening is an attempt to stop us from our efforts in the fight against terrorism, to destroy our efforts to stop the terrible criminal plan that aims to destroy what is left of our region."

The attack on the mosque began shortly after noon prayers, when militants detonated explosive devices around the al-Rawdah mosque.

Militants then opened fire on the worshippers fleeing from the blasts.

Private newspaper al-Masry al-Youm reported that more than 20 masked gunmen were involved in the attack with automatic rifles.

A three-day period of mourning has been declared for the victims. No group has yet claimed responsibility for the attack.

Egypt later said it would delay the opening of the Rafah border crossing to Gaza after the attack because of security concerns.

The crossing had been due to open for three days from this weekend.

Striking at a mosque would be a change in tactics for the Sinai militants, who have usually attacked troops, police and Christian churches.

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US President Donald Trump described the assault as a "horrible and cowardly terrorist attack" in a Twitter post.

"The world cannot tolerate terrorism, we must defeat them militarily and discredit the extremist ideology that forms the basis of their existence," he said. AAP