CAIRO - Militants shot dead five Egyptian conscripts in the Sinai Peninsula on Thursday, as the army searched for eight servicemen missing after an attack on a navy boat in the Mediterranean.

The military carried out air strikes in Sinai, killing three members of the Islamist militant group Ansar Beit al-Maqdis, security officials said.

Egypt has been hit by a wave of attacks since the army overthrew Islamist president Mohamed Morsi last year, infuriating his supporters. In Cairo, 16 people were injured Thursday in a panicked crush on a Cairo metro train after a small bomb exploded during rush hour. The attacks in Sinai, in which two police conscripts and three soldiers were taken out of their vehicles and shot dead, bore the hallmarks of Ansar Beit al-Maqdis, which often sets up impromptu checkpoints in the lawless peninsula.

The ambushes came a day after an unprecedented assault on a navy boat wounded five servicemen and left eight lost at sea.

The military, which said late Wednesday it was still conducting search and rescue operations for those missing, has called the incident a “terrorist” attack. But a day later the identities and goals of the assailants remained unknown.

A security official said that dozens of suspects rounded up at sea after the assault were still being interrogated.

It was not immediately clear whether they were “terrorists” or drug and weapons smugglers who frequent that part of the sea, he said.

Four boats used by the assailants were destroyed, according to the military.

Former French admiral Alain Coldefy told AFP that the attackers could have been militants or illegal migrant traffickers.

“It is too early to know the source of such an attack,” said Coldefy, who is now research director with the Institut de Relations Internationales et Strategiques think-tank in Paris.

“It could be terrorists, or it could have been powerful human traffickers who don’t want to be bothered in their affairs.”

A militant attack would have taken much preparation but would not have been difficult to carry out given the size of the navy boat, he said.

The Egyptian government is fighting an militant insurgency that has killed scores of policemen and soldiers, but such a maritime attack has not been seen before.

The incident came days after Ansar Beit al-Maqdis pledged its allegiance to the Islamic State militant organisation in Iraq and Syria.

Egypt’s army has launched an unprecedented crackdown in Sinai to quell the militants, razing homes along the border with Gaza to create a buffer zone with the Palestinian enclave.

One of the attacks Thursday took place at the entrance of the town of Rafah along the border with Gaza, where the army is demolishing homes to create the buffer zone.

The other occurred several kilometres (miles) to the west, in the north Sinai town of Sheikh Zuweid.

Ansar Beit al-Maqdis has spearheaded an insurgency in the peninsula that has killed scores of policemen and soldiers since the army overthrew Morsi.

It is believed to have been behind an attack on a military checkpoint last month that killed at least 30 soldiers - the deadliest such incident in years.