Saudi Arabia flag
Nine US citizens have reportedly been detained by Saudi authorities on terror chargesGetty Images

Nine American citizens are reportedly among 33 suspects who have been detained by Saudi Arabia on terrorism charges in the past week. The US embassy in the oil-rich Gulf kingdom is yet to comment on the matter.

According to a report in English-language daily Saudi Gazette, four Americans were held on 25 January and a further five were detained in the following days. The other detainees include 14 Saudis, three Yemenis, two Syrians, an Indonesian, a Filipino, a Palestinian and one citizen from the UAE and Kazakhstan each.

Saudi and US officials are still checking the names against databases, one official told the Guardian. On 29 January, four people were killed and another 18 injured when a suicide bomb blast ripped through a shia mosque in the al-Ahsa district. Sunni jihadists claimed to be behind the deadly assault.

One attacker detonated his vest at the entrance of the mosque in the eastern province when he was stopped by security. He was named as 22-year-old Abdulrahman Abdullah Sulaiman Al-Tuwaijri by Saudi Gazette. The other attacker – a 27-year-old – is yet to be named, but he was arrested after an exchange of fire and is receiving treatment for injuries.

In 2014, Riyadh classed the Islamic State (Isis) as a terrorist organisation and has held hundreds of the group's supporters. In October last year, IS (Daesh) posted a message on Twitter claiming responsibility for the death of five people who were killed after gunman opened fire at a shia meeting hall in Saihat. The attack took place just two days after the start of Ashura, the tenth day of Muharram in the Islamic calendar.

Ashura is observed by both Sunnis and Shias. Some Shias mark the event by flagellating themselves with chains and hitting their heads with swords.