Terrorists may be in the final stages of planning an attack in Saudi Arabia, the UK Foreign Office has warned.
Suicide bombers hit residential compounds in Riyadh last year
It has issued fresh guidance to travellers about the possibility of an imminent attack.
It had already warned it believed terrorists were "determined to carry out further attacks in Saudi Arabia".
The new warning comes after a British Airways flight to Riyadh, which had been due to fly on Monday afternoon, was cancelled amid security fears.
The Foreign Office website warns of "a continuing high threat of terrorism in Saudi Arabia" and advises Britons "against all but essential travel" to the kingdom.
It goes on to urge British nationals to keep a "low profile" and to "maintain a high level of vigilance, particularly in public places frequented by foreigners such as hotels, restaurants and shopping malls".
The charge d'affaires at the Saudi Embassy in London, Abdullah Al-Shahrood, said Saudi Arabia "had nothing to do" with the cancellation of the BA flight.
"We have British MPs visiting Saudi Arabia these days and the situation is stable," he told told BBC Radio 4's Today programme.
"Good intelligence we are getting will improve the situation but terrorism is an international problem. We have to have the co-operation of the international community so that we can destroy it," he said.
A similar warning to the latest one was issued by the Foreign Office at the end of December.
It warned the threat applied to but "is not limited to" residential compounds.
Accommodation in Riyadh, 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.
And co-ordinated suicide attacks on Western diplomatic compounds in Riyadh on 12 May last year left 34 dead, including the two Britons and the nine bombers.
British Airways flight 263 to Riyadh had been due to fly from London Heathrow on Monday afternoon but was grounded because of fears it could be the victim of a terrorist attack.