Saudi authorities have arrested nine American citizens among 33 “terror” suspects rounded up over the past week, AFP reported Sunday, citing the Saudi Gazette newspaper.

Four Americans were arrested last Monday and five others over the past four days, the paper reported, citing an unidentified source.

Washington, a strong ally of Riyadh, confirmed it was aware of the report but declined to elaborate.

A State Department official, speaking on condition of anonymity, told AFP, “We are aware of reports alleging that several U.S. citizens were detained in Saudi Arabia.

“The Department of State takes its obligation to assist US citizens abroad seriously. Due to privacy considerations, we have no further comment.”

The Saudi newspaper said the arrests also included 14 Saudis, three Yemenis, two Syrians, an Indonesian, a Filipino, an Emirati, a Kazakhstan national and a Palestinian.

It did not say whether any of the “terror suspects” was linked to the Islamic State (ISIS) jihadist group.

Saudi Arabia regularly cracks down on suspected Islamist terrorists, having in September arrested members of two terrorist cells in the kingdom.

ISIS has claimed responsibility for a series of bombings at Shiite mosques across the eastern part of the country over the past few months.

Saudi authorities said in July that they arrested 431 suspects connected to ISIS, their largest raid to date, and that they had foiled a number of plans for suicide attacks in Riyadh and the east.

The Saudi Gazette said some 532 ISIS suspects accused of plotting attacks in the kingdom are being questioned ahead of their trial at the criminal court in Riyadh.

They are members of six cells arrested in “pre-emptive” raids across the kingdom and include a Saudi woman and a Filipina, the paper said.