CAIRO (Reuters) - The Egyptian public prosecutor ordered that a suspected Libyan militant and 14 others be held for 15 days pending an investigation of their role in a deadly attack in Egypt’s western desert last month, state news MENA reported on Friday.

The Interior Ministry said on Thursday that Abdelrahim Mohamed al-Mesmari, from the Libyan city of Derna, was captured by Egyptian forces following an air raid in response to the attack.

Security sources initially said at least 52 policemen were killed when militants attacked a patrol, firing rockets and detonating explosives in a remote part of the desert. The Interior Ministry refuted those figures and said 16 were killed.

Charges against Mesmari will include premeditated murder of police officers, possession of firearms and joining a terrorist organization, MENA reported.

A new and little-known group called Ansar al-Islam claimed responsibility for the October attack, posing a new threat to Egyptian security forces, which have been battling an Islamic State insurgency in the Sinai peninsula since 2013.

The military last month killed 15 militants in an air raid directed at the group it blamed for the desert attack, according to the Interior Ministry, which said that all of those killed had been trained in Derna.

Mesmari escaped the air raid but was later arrested along with 29 Egyptians who had been recruited to join the group, according to the Interior Ministry.

(This version of the story corrects final paragraph to clarify that 29 suspects were arrested later, after the air strike in which 15 were killed)