"There is a continuing high threat to British nationals in the region, including Saudi Arabia. This includes attacks, either of a random nature by disaffected individuals, or by organised terrorists," it said in a statement.

The embassy encouraged Britons in the kingdom "to consider whether their presence and that of their dependents is essential" and urged those who remained to be alert and adopt a low profile.

It said a bomb threat had been made Sunday against the British School in Riyadh. While the threat "was a hoax, it reinforces the need to take security arrangements seriously," the embassy said.

Both Britain and the United States at the start of their military campaign in Iraq on March 20 urged their nationals in Saudi Arabia to increase their personal security and remain vigilant, but they did not ask them to leave.

There have been no reports of anti-Western attacks in Saudi Arabia since the war began, but security has been considerably beefed up in the capital and other main cities.

In February, the US embassy advised Americans living and working in Saudi Arabia to consider leaving in light of increased risks, and it allowed non-essential mission staff and dependents to depart.

Between 30,000 to 40,000 Americans and around 30,000 Britons live and work in Saudi Arabia.

SPACE.WIRE