Terrorists could be in the final stages of planning an attack in Saudi Arabia, the government has warned.
Alert said to be based on new information
It said: "The threat includes, but is not limited to, residential compounds."
The Foreign Office said the alert was based on new intelligence, but added: "We are not able to comment on the
nature of this information."
Terrorist attacks hit the capital, Riyadh, earlier this year and British nationals had already been warned against travel to the country.
The Foreign Office also warned the threat applied to but "is not limited to" residential compounds after accommodation, housing diplomats from the Arab world and their families, was attacked by suicide bombers on 8 November.
That attack left 18 dead as well as 120 wounded, many of them children.
Two of the bombers involved in the attack were identified by police as Saudi nationals.
Earlier this month, the US embassy warned that militants might be planning new attacks on compounds housing Westerners in Riyadh.
At the time it said that at least one compound - Seder Village - had been under "active surveillance by terrorist elements" and Britain and Australia also issued security warnings to their nationals.
That came after an attempted bomb attack on the compound was foiled by Saudi officials when they discovered a car packed with more than a tonne of explosives.
And suicide attacks on Western diplomatic compounds on 12 May left 34 dead, including the nine bombers.
Before the May attacks a number of westerners were killed or injured in a serious of smaller scale attacks.
Car and parcel bombs have been used by attackers as well as bomb attacks on shopping centres.
Back in August, UK flights to Riyadh were suspended after intelligence reports of a specific threat to British airlines flying in or out of Riyadh international airport.
Attacks hit the capital, Riyadh, earlier this year
Airport security has been further increased since those flights were resumed in September.
The Foreign Office website warns against "all but essential travel" to Saudi Arabia and that anyone still over there should "maintain a high level of vigilance, particularly in public places frequented by foreigners".