A suicide bomber rammed his explosive-laden car into a convoy of buses carrying off-duty soldiers in Egypt's turbulent region of northern Sinai on Wednesday, killing 11 and wounding 37, security and military officials said.

The bombing was the latest in a wave of attacks against the military and security forces in a burgeoning insurgency in the Sinai Peninsula blamed on Islamic militants that has mounted since the military's ouster of Islamist president Mohammed Morsi in July.

The bomber struck as the convoy of four army buses was travelling on the road between the border town of Rafah and the coastal city of el-Arish, military spokesman Col. Mohammed Ahmed Ali said.

The soldiers belong to the 2nd Field Army, which is doing most of the fighting against Islamic militants waging an insurgency against security forces in Sinai. The buses were on their way to Cairo, military officials said, speaking on condition of anonymity as they weren't authorized to release the information.

"The precious blood of our sons strengthens our resolve to cleanse Egypt and shield its sons from violence and treacherous terrorism," Ali wrote on his Facebook page.

There was no immediate claim of responsibility for Wednesday's attack, but suicide car bombings are a signature method of militant groups linked to or inspired by al-Qaeda.

The northern Sinai, which borders Gaza and Israel, has been restless for years, but attacks have grown more frequent and deadlier since the coup that removed Morsi. The attacks have also grown more daring: In August, gunmen pulled 25 police conscripts off minibuses in the Sinai and shot them dead on the side of the main road linking Rafah to el-Arish.

Attacks have spread outside northern Sinai

The attacks have also spilled over elsewhere in Egypt, including in the southern part of the peninsula — and in the capital, Cairo.

Hunt for 'moles' inside government

The recent surge in violence has prompted a shakeup within security agencies' ranks, including a hunt for possible Islamist "moles" amid officials' suspicions that Morsi's Muslim Brotherhood is linked to the violence - an accusation the group denies.

Nearly two dozen employees with sensitive posts in the Interior Ministry, which is in charge of police, are being probed for Brotherhood sympathies or for providing information to the group, according to senior security and military officials. Also, security officials who were removed or transferred from key positions during Morsi's year-long presidency are being reinstated, according to the officials, who spoke on condition of anonymity to talk about the agencies' workings.

-Associated Press

Earlier this week, a senior security officer who monitors Islamist groups, including Morsi's Muslim Brotherhood, was shot dead as he drove in Cairo's eastern Nasr City district. In September, the interior minister, who is in charge of the police, survived an assassination attempt by a suicide car bomb.

In a video clip posted Tuesday on the internet, a militant group, Ansar Jerusalem, claimed responsibility for this week's slaying of the security officer, police Lt. Col. Mohammed Mabrouk. Ansar Jerusalem said the killing was in retaliation for the recent arrest of female Morsi supporters.

The group had previously claimed responsibility for the attempt on the interior minister's life and an attack on military intelligence compounds in the Suez Canal city of Ismailia and the southern Sinai city of Tor.

For several months, the military has been carrying out intensified raids in the towns and villages of northern Sinai, hunting for militants.

The northern Sinai region, which borders Gaza and Israel, has been restless for years. But attacks have grown more frequent, deadlier and bolder since Morsi's ouster.

In August, gunmen pulled 25 police conscripts off minibuses in the Sinai and shot them dead. There have also been a number of suicide attacks — a tactic rarely seen during the 1990s Islamic insurgency. 

Meanwhile, clashes late Tuesday between revolutionary youths opposed to military rule and police killed two people, including a teenager, said Ahmed el-Ansari, head of Egypt's emergency services. He said the teenager suffered a head wound from a birdshot pellet and died while being taken to hospital. The second, a 23-year-old man, died from a gunshot wound to the head, he said.

The violence in Cairo's famed Tahrir Square followed daylong protests marking the second anniversary of clashes between protesters and police on an adjacent street. A joint police and army contingent cleared the square of protesters late Tuesday.

On Wednesday at dawn, assailants threw a grenade at a police checkpoint in a northern Cairo suburb, injuring four policemen, security officials said. The assailants fled the scene, the officials said.

Authorities have since Morsi's ouster waged a major crackdown against the Brotherhood, arresting some 2,000 top and middle-level members and several thousand followers. Hundreds were killed when security forces cleared two protest camps of Morsi supporters in August.

Morsi, along with the group's top leaders, are in detention and face trials on charges that vary from murder and inciting murder to conspiring with foreign powers and corruption.

Supporters of the former president have staged near-daily protests against the July 3 coup, mostly in universities. The number of protesters, however, has been dwindling, although they occasionally mass several thousand.