At least 27 soldiers have been killed in an attack on an army checkpoint in Egypt's North Sinai, state media has reported.

The attack on Friday afternoon hit an army checkpoint at Karm al-Qawadeis, southwest of Sheikh Zuweid.

Egyptian sources told Al Jazeera that a suicide car bomber detonated his explosives near the checkpoint's magazine, causing it and an army vehicle to explode. Fighters then attacked the site with guns and a rocket-propelled grenade.

The source said the group attacked as soldiers were on break inside their tents. State media reported that 28 people were wounded, several of whom were in critical condition. 

"Most have been seriously injured and not all of them have been taken to hospital yet," health ministry official Tareq Khater told the AFP news agency.

Three more members of Egypt's security forces were killed in a separate attack at a checkpoint outside nearby al-Arish. It was not immediately clear whether the dead were soldiers or police.

The Egyptian president, Abdel Fattah el-Sisi, announced three days of national mourning after the attack, and promised to eradicate those responsible.

Local media said the president also ordered a meeting of the government's national defence council following the blast.

The council is made up of the prime minister, the head of the parliament, the minister of defence and the commanders of the Egyptian armed forces, and is chaired by the president.

The attack was one of the deadliest on security forces since Sisi in July last year overthrew Mohamed Morsi from the presidency, launched a bloody crackdown on his supporters and declared his Muslim Brotherhood movement a terrorist organisation.

Hundreds of soldiers and police officers have been killed in attacks.

Source: Al Jazeera and agencies