Two suspected Islamic State militants were killed and three were arrested by Saudi security forces in co-ordinated raids in the capital Riyadh and the eastern city of Dammam, the Interior Ministry said on Monday.

The statement carried by state news agency SPA said the men belonged to an Islamic State cell that was planning to carry out "an imminent terrorist act" and that one of the sites raided by the authorities was a bomb-making factory.

Islamic State has called on supporters to carry out attacks in Saudi Arabia and string of deadly attacks by its followers has fuelled concerns about a growing threat of militancy in the world's top oil exporter.

Saudi authorities said on Saturday they killed an 18-year-old suspected member of the group and arrested his brother after the brothers abducted a cousin and filmed his execution, and killed three other people, in the country's desert northern province of Ha'il.

An Islamic State suicide bomber killed at least 15 people in an attack on a mosque used by members of a local security force in southwest Saudi Arabia last month, and other bombings by the group on Shi'ite mosques in the kingdom and neighbouring Kuwait killed dozens of worshippers this summer.

Saudi authorities say they are cracking down on the militants and announced in July that it had detained 431 people suspected of belonging to the organisation.-Reuters