Egyptian President Abdel-Fattah al-Sisi (C) chairs a meeting of the security committee,which is attended by the ministers of defense and interior in addition to the heads of general intelligence and military intelligence services, on the attack on a mosque, Cairo, Egypt, Nov. 24, 2017. The death toll in an attack on Friday on a mosque in Egypt's North Sinai province rose to 235, Egypt's state TV reported. (Xinhua Photo)

CAIRO, Nov. 24 (Xinhua) -- Egyptian president Abdel Fattah al-Sisi vowed on Friday a "fierce action" will be carried out in response to a mosque's attack in North Sinai province that left at least 235 killed, state-run TV reported.

"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.

"Such attack is aimed at destroying our unity, but it will steel our resolve to defeat terrorism," he added.

Earlier the Egyptian presidency declared a three-day mourning period across the nation.

An explosive device planted outside the mosque near Arish city went off, before militants opened fire at the prayers, an official security source told Xinhua.

The attack occurred in the village of Rawda in Beir el-Abad, 40 km from Arish, the source added.