RIYADH (AFP) ― Saudi Arabia said Sunday it has arrested 135 suspects for “terrorism” offenses, after the kingdom’s participation in air strikes against Islamic State group extremists raised concerns about possible retaliation.

The suspects include 26 foreign nationals, among them “16 Syrians and three Yemenis,” Interior Ministry spokesman Gen. Mansour al-Turki said, cited by the Saudi Press Agency.

The detainees belong to “suspect groups ... that terrorism united,” and their arrests followed “repeated attempts to harm the security and stability of the homeland,” Turki said without specifying when they were detained.

Forty of the suspects had gone to “zones of conflict, joined extremist groups and trained in the handling of weapons ... before returning to the kingdom to destabilize the country,” Turki said.

He added that 54 others were implicated in the “financing, recruitment, propaganda and manufacture of explosives ... in aid of extremist groups.”

Seventeen suspects were linked to unrest and armed attacks on security forces in Awamiya, a community in Eastern Province just west of Dammam city.

Awamiya has been a focus for clashes between security forces and minority Shiite protesters.

Turki said the detained foreign suspects included an Egyptian, a Lebanese, an Afghan, an Ethiopian, a Bahraini and a stateless person.

The arrests come as Saudi Arabia, the United Arab Emirates, Jordan and Bahrain take part in U.S.-led air strikes against the IS extremist group in Syria.

Saudi pilots who took part in the initial air raids in September received online death threats after photos were published of those involved, among them a son of the crown prince.

The kingdom’s Grand Mufti Sheikh Abdul Aziz al-Sheikh has said al-Qaida and IS “have nothing to do with Islam and (their proponents) are the enemy number one of Islam.”

Last week an IS-linked media group released a video claiming to show the shooting in Riyadh of a Danish national by its “supporters,” the U.S.-based monitoring group SITE said.

Denmark has confirmed that one of its citizens was shot and wounded in the Saudi capital on Nov. 22.

The video carries an audio recording, allegedly of IS leader Abu Bakr al-Baghdadi saying that Saudi rulers will see “no more security or rest.”

A week after the Dane was shot, someone stabbed and wounded a Canadian while he shopped at a mall in Dhahran on Saudi Arabia’s Gulf coast.

Police arrested a Saudi suspect.

A source familiar with the situation said last week that they were “still trying to figure out what the motive is,” but many people were wondering if the attacks signaled a trend.

In October, a Saudi-American former employee of a U.S. defense contractor shot dead an American colleague and wounded another in Riyadh.

The suspect had recently been fired, officials said.

That was the first deadly strike against Westerners in Saudi Arabia since several were killed in a wave of al-Qaida violence between 2003 and 2007.

Both Canada and Denmark are among the Western states taking part in an aerial campaign against IS in Iraq.

In November, Saudi Arabia blamed IS-linked suspects for the killing of seven Shiites, including children, in Eastern Province.

Security forces in the Sunni-dominated kingdom arrested 73 Saudis and four foreigners in connection with the attack, the interior ministry has said, adding that the head of the criminal network behind the murders “had links with Daesh,” the Arabic name for IS.

The ministry added that security forces seized documents and electronic equipment that “revealed contact between this terrorist organization and Daesh abroad.”