Police in London said on Thursday they had thwarted a major terrorist plot to blow up aircraft in mid-flight while Home Secretary John Reid called the plot a "major threat to the UK and international partners."

British MI5 and police had foiled an attempt to detonate explosives devices smuggled aboard as hand luggage on mid-night flights from Britain to the United States, Reid said Thursday morning.

"Overnight the police, with the full knowledge of ministers, have carried out a major counter-terrorism operation to disrupt what we believe to be a major threat to the UK and international partners," he said.

"The police, acting with the Security Service MI5, are investigating an alleged plot to bring down a number of aircraft through mid-flight explosions, causing a considerable loss of life," he said.

Earlier Thursday, Scotland Yard also said that the aim of the plot was to detonate explosive devices on board the aircraft in hand luggage. The plot was likely to target flights from Britain to the United States, it said.

Responding to the incident, Britain's Joint Terrorism Analysis Centre raised the country's security threat level to "critical" from "severe."

Britain has a five-level rating for security threats, ranging from low to critical, which is the highest level

Security at the airports across the country has beefed up, and massive delays have been caused at all airports cross Britain. About 18 people had been arrested so far in and around London, according to a BBC report.

British Airways (BA) on Thursday advised all passengers that they would not be permitted to carry any hand baggage on board any aircraft departing from any airport in Britain.

Passengers will be allowed to take only travel documents, eyeglasses and a handful of other items through airport security, the company said in a statement.

BA also advised passengers that no electrical or battery powered items including laptops and mobile phones could be allowed in the cabin.

Meanwhile, The Downing Street said that Prime Minister Tony Blair, on holiday in the Caribbean, is in constant contact with the UK anti-terror team. The operation undertaken is with full support from the prime minister, it said.

Blair also kept U.S. President George W. Bush informed on security threat to planes, the Downing Street added. The United States has raised threat level in response to the terror plot in Britain.

Source: Xinhua