RIYADH (Reuters) - Saudi Arabia's security services have detained a Saudi Arabian man on suspicion of shooting dead two policemen and wounding two others in separate attacks in Riyadh on Wednesday and in March, state media reported on Saturday, citing the Interior Ministry.

Police found the weapon and car used for the shootings at the home of Rami Abdullah Thulab al-Shammari, according to a ministry statement published by state news agency SPA on Saturday.

Last year militant group Islamic State called on sympathisers in the kingdom to assassinate members of the security services or governnment, non-Muslim residents and members of the Shi'ite Muslim minority. Al Qaeda has also vowed to bring down Saudi Arabia's ruling family.

Although the conservative Sunni Muslim kingdom imposes a version of sharia law supported by jihadists, the ruling family are seen by some as having betrayed Islam through having strong ties with Western countries.

Three other Saudi citizens and two Yemenis, one of whom was living in the kingdom illegally, have also been detained on suspicion of trying to help Shammari flee the country. He was detained in Jizan province close to the border with Yemen, the Interior Ministry said.

Riyadh's police spokesman said on March 30 that shots fired from an unidentified car had injured two policemen in a patrol car late the previous night, and said on Wednesday that two policemen had been killed after a similar attack.

(Reporting by Angus McDowall; Editing by Louise Ireland)