Women walk past rubble of damaged buildings in Raqqa, Syria May 14, 2018. REUTERS/Aboud Hamam

BEIRUT (Reuters) - Security forces in northern Syria’s Raqqa city said on Sunday they had uncovered an Islamic State sleeper cell which was plotting series of large attacks across the devastated city.

Raqqa served as the de facto capital of Islamic State’s self-proclaimed caliphate until it was retaken by the Kurdish-led Syrian Democratic Forces (SDF) militia alliance last October.

A spokesman for the Raqqa Internal Security Forces set up by the SDF said it had killed two members of an Islamic State cell and detained five others during an operation on Saturday.

“Special forces and explosives experts carried out a counter operation .. to confront plans which were about to be executed by a terrorist cell affiliated with mercenaries of Daesh in a neighborhood in Raqqa city,” the unit’s spokesman Mohannad Ibrahim said at a news conference.

Daesh is an Arabic acronym for Islamic State.

The forces raided two residential apartments where the cell members were hiding and confiscated grenades, pistols and explosives, the spokesman said.

They also found a car bomb at the site of the operation and unearthed a large cache of arms and land mines buried nearby.

The city has witnessed lately a wave of road side bombings targeting mainly SDF officials and fighters.

In June, SDF imposed a three-day curfew in Raqqa and declared a state of emergency saying Islamic State militants had infiltrated the city and planned a bombing campaign.