The remains of a Russian airliner which crashed is seen in central Sinai near El Arish city, north Egypt, October 31, 2015. REUTERS/Stringer

CAIRO (Reuters) - The Egyptian-led committee investigating the crash of a Russian passenger plane in the Sinai Peninsula last October said on Thursday it was referring the case to Egypt’s attorney general, the first indication that it suspects foul play.

Last month Egypt’s President Abdel Fattah al-Sisi said he believed terrorists had downed the plane in order to damage the country’s tourism industry and its ties with Moscow.

Russia and Western countries have long said they believe the flight was brought down by a bomb smuggled on board, but the committee investigating the issue has never acknowledged evidence of foul play.

After receiving a report on the crash from Russia suggesting suspected criminal activity this week, the committee decided to refer the case to the attorney general, it said in a statement.

Egypt is battling an insurgency concentrated in northern Sinai and waged by Islamic State’s Egyptian branch Sinai Province. The insurgency has killed hundreds of soldiers and police.

The Islamic State said it had smuggled an explosive aboard the Russian jet inside a soft drink can. An EgyptAir mechanic whose cousin joined Islamic State in Syria is suspected of planting the bomb, sources familiar with the matter told Reuters in January.

On Thursday five Egyptian soldiers were killed and 10 injured when militants fired mortars into a military base in the northern Sinai city of Rafah, one of which landed in a weapons cache and set off an explosion, security sources said.

In a separate statement the military said three soldiers had been killed during a military operation in north Sinai. The discrepancy in numbers could not immediately be accounted for.

The Russian plane crash has called into question Egypt’s campaign to eradicate Islamist militancy and has harmed its tourism industry, a cornerstone of the economy.