British Airways has suspended all flights to Saudi Arabia until further notice, in response to a specific terrorist threat to its planes in the country.
Several passengers were stranded at Heathrow by the news
The threat, announced on Wednesday, is not thought to be related to the missile arrests in the United States.
Meanwhile, the US renewed its warning for its citizens to avoid non-essential travel to Saudi Arabia.
The State Department said the government had received indications of terrorist threats aimed at American and Western interests, including the targeting of transport and civilian aircraft.
BA's decision follows advice from the Department for Transport.
A spokesman for the department said it had warned airlines there was "credible intelligence of a serious threat to UK aviation interests in area".
The source of the scare lies in the Saudi capital Riyadh, where the authorities have been trying to break up Islamist terror cells, said BBC security correspondent Frank Gardner.
The security forces have had several gun battles in recent days - in which three police officers have been killed and a number of militants captured.
"By watching Riyadh airport they've learned this week that al-Qaeda sympathisers also had the airport under surveillance," said our correspondent.
"They learned of a plot to attack a British target, thought to be an aircraft."
BA usually operates four flights a week each to the Saudi cities of Riyadh and Jeddah.
Other airlines, including Saudi Arabian Airlines which flies direct to Riyadh, and several other Middle Eastern airlines which have indirect routes, are still flying to Saudi.
Business analysts said that the news would be unlikely to affect BA shares, which had been hard hit by the recent wildcat strike at Heathrow.
Passengers at Heathrow, some of whom were on their way to Mecca, were dismayed to find out that their flights were cancelled - and many heard through the assembled media rather than the airline.
Mohammed Rauf Khan, who had travelled down from Bradford told BBC News Online: "I'm very upset. I think they could have said something beforehand. It's not right that I should find this out from a journalist."
Nadia Talpur, 20, a student from Toronto, Canada, who was also flying to
Jeddah to see relatives said: "I have been passed round three different people
so far and I still don't know what's going on. I'm about ready to explode.
"I know there's nothing they can do about security but all I want to know is
how to get another flight."
Whitehall officials told the BBC the terrorist threat warning was issued by JTAC, the government's new Joint Terrorism Assessment Centre in London.
The Foreign Office said it would alert the British community in Saudi Arabia to the announcement, via its warden network.
It said it did not intend to change its current advice about travel to Saudi Arabia. This already advises against all but essential travel to the Middle East country.
It states: "If you choose to travel to, or remain in, Saudi Arabia you should take all necessary steps to protect your safety and should make sure you have confidence in your security arrangements."
Bomb attacks in Riyadh on 12 May this year killed more than 30 people, including two British nationals, and injured nearly 100.
The advisory warns: "Further large or small scale attacks against Western interests in Saudi Arabia remain likely.
"You should maintain a high level of vigilance, particularly in public places
frequented by foreigners such as hotels, restaurants and shopping malls."
Prior to the May attacks, a number of British nationals and other Westerners died or were injured in a series of smaller scale bombings and shootings in Riyadh and al Khobar.
BA ceased flights to Nairobi on 15 May this year, after the government ordered a ban on all UK airline flights to and from the African country.
This also followed a specific threat against UK planes in the region. The Nairobi suspension was lifted a month later.
But UK flights to and from the Kenyan coastal town of Mombasa have not yet resumed.
Passengers seeking information on BA flights to Saudi Arabia can ring the airline's main number on: 0870 8509850.