DUBAI (Reuters) - Saudi Arabia has arrested the four main suspects in an attack on Shi'ite Muslims this month and believes it was ordered by Islamic State militants from abroad, the state news agency cited an Interior Ministry security spokesman as saying on Monday.
Seven members of the Sunni-ruled kingdom's Shi'ite minority were shot dead in the Eastern Province district of al-Ahsa on Nov. 3 as they marked their holy day of Ashoura.
Saudi Arabia, the world's top oil exporter, put down an upsurge of Islamist militancy a decade ago, but fears that jihadist groups such as Islamic State or the al Qaeda affiliate Nusra Front now operating in Syria or Iraq will radicalise Saudis to mount a new wave of strikes inside the kingdom.
Last week, the ministry said militants were trying to attack Saudi Arabia, but that it was not aware of any evidence that the al-Ahsa attack had been coordinated with Islamic State.
On Monday, the ministry spokesman said 77 suspects had been arrested so far, and that they were believed to include the four main perpetrators.
He said the leader of the al-Ahsa attack had received orders from abroad, and that "the target, as well as those to be targeted and the timing were all specified for him, as well as the provision that the (attack) be carried out in al-Ahsa".
The leader had picked three followers, and these had scouted out the target, seized a car, killed its owner, and used it in the attack.
The spokesman said security forces carried out operations "to arrest everyone affiliated with this terrorist group, whether those who pledged allegiance to the leader of the group, or participants, supporters, financiers, or those who provide cover".
Two Saudis and a Qatari were killed as they resisted arrest, along with two security officers, the ministry said.
Authorities had already said that among the detainees were people believed to have fought for Sunni jihadists in Syria or who had previously been jailed for fighting for al Qaeda.
As the birthplace of Islam and a champion of conservative Sunni doctrine, Saudi Arabia is an important ally for Western countries battling Islamic State, and its monarchy a symbolic target for the militant group itself.
Although it has backed rebel groups fighting alongside jihadis against Syrian President Bashar al-Assad, Saudi Arabia has also taken steps to stop its citizens joining militants in Syria or Iraq, or giving them money.
(The story refiles to amend phrasing of quote in 8th paragraph.)
Reporting by Ali Abdelaty in Cairo, Writing by Yara Bayoumy in Dubai, Editing by Kevin Liffey