Saudi Arabia's news agency says authorities have uncovered "terrorist" cells plotting attacks against Saudi police and civilians in Riyadh, the capital.

The Saudi Press Agency quotes an unidentified Interior Ministry official as saying that six Yemenis have been arrested after they prepared explosives and experimented with them outside Riyadh. Explosives were seized, the report says.

The official referred to the suspected terrorists as belonging "deviant group," a common Saudi description of al-Qaida.

"The terrorist cell in Riyadh promoted the deviant Takfiri thought," the statement said, in reference to an al-Qaida-like extremist ideology.

The Sunday report said they were connected to "suspected elements" inside and outside the kingdom.

Saudi Arabia has been cracking down on Islamic militants since al-Qaida launched a wave of attacks in the country in 2003, killing dozens.