The US embassy in Saudi Arabia says has suspended consular services in the kingdom for two days due to "heightened security concerns", after warning of threats against Western oil workers.

All services in Riyadh and at the consulates in Jeddah and Dhahran have been cancelled for Sunday and Monday, it said in a statement posted on its website on Saturday.

The embassy warned US citizens to take extra precautions and keep a low profile if they were out in public.

"All US citizens are encouraged to be aware of their surroundings, and take extra precautions when travelling throughout the country," it said.

"The Department of State urges US citizens to carefully consider the risks of travelling to Saudi Arabia and limit non-essential travel within the country."

The embassy on Friday had warned that Western oil workers risked being attacked or kidnapped by "terrorist" groups.

It did not identify the source of the threats and said no details were available on the planned attacks.

Saudi Arabia is taking part in US-led air strikes that began in September against the Islamic State of Iraq and the Levant (ISIL) group in Syria, raising concerns about possible retaliation.

Westerners in Saudi Arabia have come under attack four times since October.

The latest was last month when US defence contractor Vinnell Arabia said two of its American employees were shot at in Eastern Province, where most of the kingdom's oil wealth is concentrated.

Saudi police said that one of them was wounded but results of the investigation that followed have not yet been revealed.

In October, another Vinnell employee was shot dead and another wounded at a petrol station in Riyadh, in what Saudi authorities have said was not a "terrorist-related" incident.

A Dane was wounded in November as he was driving away from his workplace when he was fired upon from another car.

Authorities said the three Saudis arrested on suspicion of involvement in that attack had acted "in support of" ISIL.

A week after the Dane's shooting, a Canadian was stabbed and wounded while he shopped at a mall on Saudi Arabia's Gulf coast.

Shia-populated Eastern province is also the scene of unrest sparked by members of the minority who occasionally clash with police.

Saudi Arabia has also blamed ISIL-linked suspects for the November killing of seven members of the Shia community in Eastern Province, including children.

Several Westerners in Saudi Arabia were killed in a wave of al-Qaeda attacks between 2003 and 2006.