The Foreign and Commonwealth Office on Saturday advised British nationals against all but essential travel to Saudi Arabia.

"Following terrorist attacks in Riyadh in May and November, we continue to believe terrorists are planning further attacks in Saudi Arabia," said its statement, posted on the website of the British embassy in Riyadh. 

The Foreign Office said the "terrorist threat across Saudi Arabia remains high", referring to an announcement by Saudi authorities on Tuesday that they had foiled a car bombing and killed two of the "terrorists" involved in the plot. 

"You should adopt a low profile and avoid public gatherings which could lead to disorder"

Foreign and Commonwealth Office

A Saudi security source was quoted by a local newspaper on Wednesday saying the explosives seized in the operation were enough to "blow up a whole district".

It added the target was similar to the 9 November bombing of the al-Muhaya residential compound which killed at least 18 people and was blamed on the al-Qaida network. 

Vigilance

Britain warned its 30,000 citizens in Saudi Arabia to be highly vigilant in public places such as hotels, restaurants and shopping malls. 

"You should adopt a low profile and avoid public gatherings
which could lead to disorder," said the Foreign Office. 

Britain first issued its travel warning for Saudi Arabia on
24 October following similar warnings by Australia and the United States.