Police and troops have been put on "maximum alert" for the duration of Operation Sinai 2018, the army said in a statement.

The goal is to tighten control of border districts and "clean up areas where there are terrorist hotbeds".

The security forces have been increasingly targeted by jihadists since the army overthrew Islamist president Mohamed Morsi in 2013.

Most of the violence has been in North Sinai province, but there have also been attacks on the military, police and even churches elsewhere, including Cairo.

In November, President Abdel Fattah al-Sisi, who is seeking re-election in polls next month, ordered the armed forces chief of staff to restore security in Sinai within three months after militants killed more than 300 worshippers at a mosque.

Jihadists have also attacked tourists, killing all 224 on board a Russian plane carrying holidaymakers in 2015.