A co-ordinated assault on an army checkpoint in the Sinai Peninsula killed 30 Egyptian troops on Friday, making it the deadliest single attack in decades on the military, which has been struggling to stem a wave of violence by Islamic extremists since the overthrow of Islamist President Mohammed Morsi.

Officials described it as "well-planned" attack that began with a car bomb which may have been set off by a suicide attacker. Other militants then fired rocket-propelled grenades, striking a tank carrying ammunition and igniting a secondary explosion. Roadside bombs intended to target rescuers struck two army vehicles, seriously wounding a senior officer.

State-run TV said there was an explosion followed by clashes between troops and militants, without providing further details. The attack took place some 15 kilometres from the northern Sinai city of el-Arish, in an area called Karm el-Qawadees.

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There was no immediate claim of responsibility, but the country's most active militant group — named Ansar Beit al-Maqdis, or Champions of Jerusalem — has claimed a string of past attacks on security forces.

The officials said the death toll is expected to rise because 28 people were wounded and several were in critical condition.

Egypt's President Abdel-Fattah el-Sissi, the former defence minister and army chief who overthrew Morsi last year, held an emergency meeting of the National Defence Council and declared a three-day mourning period. El-Sissi has said in the past that the militants hide in populated areas, making it difficult for the military to combat them.

An official said the government is considering the eviction of residents living in small villages that are considered the "most dangerous" militant bastions and declaring certain areas to be closed military zones. All officials spoke on condition of anonymity because they were not authorized to talk to media.

Egypt's official news agency MENA said military helicopters ferried the dead and wounded to Cairo hospitals. Egypt's top Islamic authority, Grand Mufti Shawki Allam, condemned the attacks and said those who carry out acts of terrorism "deserve God's wrath on earth and at the end of days."

Islamic militants have been battling security forces in the Sinai for a decade, but the violence spiked after the military overthrew Morsi in July 2013 amid massive protests demanding his resignation. The attacks have also spread to other parts of Egypt, with militants targeting police in Cairo and the Nile Delta.

The government has blamed the violence on Morsi's Muslim Brotherhood group and launched a sweeping crackdown against his supporters, killing hundreds in street clashes and jailing some 20,000 people. Authorities have tried to link the group to Ansar Beit al-Maqdis by airing confessions of people alleged to belong to both.

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The Brotherhood officially renounced violence decades ago and has denied involvement in the recent attacks, saying it is committed to peaceful protests demanding Morsi's reinstatement.

Ansar Beit al-Maqdis claimed responsibility for a car bomb attack on a security headquarters in the Nile Delta city of Mansoura which killed 16 people, almost all policemen, in December 2013. It also claimed the attempted assassination of Egypt's interior minister in September of that year.

Authorities say it was also responsible for the killing of 25 policemen who were bound and blindfolded before being shot dead on a Sinai roadside in August 2013. The government also blamed the group for an attack on Egyptian troops patrolling the remote western border with Libya in July, which left 22 soldiers dead. No one claimed either attack.

In January Ansar Beit al-Maqdis released a video of its fighters downing a military helicopter over Sinai with a shoulder-fired missile, an attack that killed all five crewmembers and raised concern over the group's growing military prowess.

The group was initially inspired by al-Qaida, but in recent months it has expressed affinity with the al-Qaida breakaway group that refers to itself as the Islamic State, and which controls large parts of Syria and Iraq. In January, the leader of Ansar Beit al-Maqdis, Abu Osama al-Masri, praised the Islamic State in a recording posted on jihadi forums.

Sinai-based militants have exploited long-held grievances in the impoverished north of the peninsula, where the mainly Bedouin population has complained of neglect by Cairo authorities and where few have benefited from the famed tourist resorts in the more peaceful southern part of Sinai. The police in northern Sinai largely fled during the 2011 uprising that toppled President Hosni Mubarak, as militants attacked stations and killed scores of security forces.

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Egypt has a long history of Islamic militancy. Former President Anwar Sadat was assassinated by Islamic militants in 1981, and extremists carried out a wave of attacks targeting security forces, Christians and Western tourists during the 1990s.