MOSCOW (Reuters) - Russia’s Federal Security Service (FSB) said on Friday it had detained five members of an Islamic State cell planning attacks in several regions and had seized an array of weapons, according to Russian news agencies.

The five suspects were apprehended in the city of Yaroslavl, northeast of Moscow, on May 3-4, the Interfax news agency reported, quoting an FSB statement.

Russia, whose military is helping the Syrian government fight rebel forces and Islamic State militants, is hosting the soccer World Cup next month and is increasing security measures.

On April 27, the FSB said it had thwarted an Islamic State plot to carry out a series of high-profile attacks in the Moscow area, where soccer World Cup matches are due to take place this summer.

The FSB on Friday did not reveal the identities of the detained or provide details on when or where the attacks were meant to take place.

“In the course of house searches, an arsenal of home-made explosive devices and substances, firearms and ammunition were seized from the detained,” the FSB was quoted as saying.

Their activities were being coordinated partly from abroad using the Telegram instant messaging service, which Russia moved to block last month, the FSB statement said.

Separately, the Roskomnadzor watchdog blacklisted Telegram after it refused to comply with a court order to grant security services access to its user-encrypted messages.

The FSB has said it needs to access some user messages for its work, although supporters of Telegram - thousands of whom rallied against the ban in Moscow this week - say the move amounts to an attack on Internet freedoms.