Saudi Arabia has put security forces on alert for a possible militant attack on a shopping mall or energy installation, Interior Ministry spokesman Mansour Turki said on Monday.

"There was information about a possible act targeting a mall or Aramco installations. We passed this information to the security forces to be on alert," he told Reuters.

Turki said he had no further information about the threat. Saudi Arabia, the world's biggest oil exporter and key strategic ally of the United States, has been a target of jihadist militant groups for years, including al Qaeda and Islamic State.

Riyadh has been carrying out air strikes against Iran-allied Houthi rebels in neighbouring Yemen since March 26 in a conflict in which nine members of its security forces have been killed by cross-border fire.

This month Saudi police announced they had detained a Saudi citizen suspected of shooting dead two police officers and injuring two others in two separate attacks in Riyadh.

"Saudi Arabia is targeted by terrorism. Usually in such situations (conflicts), there are attempts by terrorist groups to take advantage and carry out attacks," said Turki.

On Saturday, guards at the gates of a central Riyadh shopping mall stopped single men from entering and searched the bags of female shoppers, Reuters reporters said.

In 2006, four al Qaeda militants breached the gates of Saudi Aramco's Abqaiq plant but did not manage to cause significant damage before being killed in a shootout with security guards, Saudi authorities said.

However, a US diplomatic cable from the same year released by WikiLeaks quoted the then-U.S. ambassador as saying he understood that "the attack on Abqaiq had been much closer to succeeding than generally acknowledged".

At the time, Abqaiq processed 70 per cent of Saudi crude.

Subsequent US cables documented American assistance to the Saudis in strengthening the security of energy infrastructure, including the establishment of a dedicated, 40,000-strong Facilities Protection Force.- Reuters