Egypt’s President El-Sisi, declaring the country faces a threat to its existence from “terrorists”, has blamed a “foreign-funded operation” for Friday’s attacks that killed 31 soldiers in the Sinai Peninsula.

Speaking before the funeral for the slain troops, Sisi said the foreign powers want to “break the back of Egypt”: “There is a big conspiracy against us.”

He said Cairo is in an “extensive war” that will last a long time.

On Friday, 28 soldiers were killed by a car bomb near Sheikh Zuweid, close to the border with Gaza. Another three security personnel were killed at a checkpoint by gunmen.

Following the attack, Sisi declared a state of emergency for three months and imposed a 5 pm to 7 am curfew in North Sinai.

No one has claimed the latest attacks, but previous operations have been carried out by the Islamist faction Ansar Beit al-Maqdis.

The Egyptian regime has blamed much of the violence on the Muslim Brotherhood, declared a “terrorist group” last year, but the Brotherhood condemned the “new massacre” and offered condolences to the “families of the martyrs and victims of the treacherous coup”.

It said the killings “added to the black record of the military junta that has thrown the army into the political arena and put the Sinai under siege, isolation and schemes of displacement”.