Riyadhi, Saudi Arabia ? Saudi security forces arrested 42 suspected terrorists, including four foreign nationals, allegedly involved in earlier attacks across the kingdom, the Interior Ministry said Saturday.

On Friday, Saudi security forces killed six suspected al-Qaida members and arrested a seventh following a shootout in the capital, Riyadh. One policeman was killed.

Saudi Arabia, a U.S. ally, launched an aggressive anti-terrorism campaign in May 2003 after suicide bombers linked to al-Qaida attacked three residential compounds in the capital, Riyadh.

Hundreds have been detained in the campaign, which has managed to capture or kill most of those named on the kingdom’s two most-wanted lists.

The 42 suspects are said to belong to a group inspired by “takfiri doctrine,” which maintains that those not adhering to its particular fundamentalist vision of Islam are considered “infidels.”