Western oil workers in Saudi Arabia risk being attacked or kidnapped by "terrorist" groups in the OPEC kingpin, the US embassy in Riyadh said in a warning posted online.
The US mission said it "has information stating that, as of early March, individuals associated with a terrorist organisation could be targeting Western oil workers, possibly to include those US citizens working for oil companies in the Eastern Province, for an attack(s) and/or kidnapping(s)".
The statement, which was published on the embassy website late on Friday, 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 jihadist 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" the Islamic State group.
A week after the Dane's shooting, someone stabbed and wounded a Canadian while he shopped at a mall on Saudi Arabia's Gulf coast.
"All US citizens are encouraged to be aware of their surroundings, and take extra precautions when travelling throughout the country," said the US embassy, urging citizens to "carefully consider the risks of travelling to Saudi Arabia".
Shiite-populated Eastern province is also the scene of unrest sparked by members of the minority who occasionally clash with police.
In January last year, gunmen attacked the car of two German diplomats, who escaped unharmed.
Saudi Arabia has also blamed IS-linked suspects for the November killing of seven members of the Shiite community in Eastern Province, including children.
Several Westerners in Saudi Arabia were killed in a wave of deadly Al-Qaeda attacks between 2003 and 2006.