The United States early on Thursday raised its security threat level to the highest level for commercial flights from Britain to the United States in response to an aborted major terror plot in Britain.

"For that reason, the United States government has raised the nation's threat level to Severe, or Red, for commercial flights originating in the United Kingdom bound for the United States," said a statement from the U.S. Department of Homeland Security.

Police in London said early on Thursday they had thwarted a major terrorist plot to blow up aircraft in mid-flight.

Police said the aim of the plot was to detonate explosive devices on board the aircraft in hand luggage, and it was likely to target flights from Britain to the United States.

Security has been beefed up at airports across Britain. A total of 18 people had been arrested so far in and around London, according to a BBC report.

"We believe that these arrests (in London) have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," the U.S. Department of Homeland Security said.

"To defend further against any remaining threat from this plot, we will also raise the threat level to High, or Orange, for all commercial aviation operating in or destined for the United States," the statement said.

"Currently, there is no indication ... of plotting within the United States," it said.

"Consistent with these higher threat levels, the Transportation Security Administration is coordinating with federal partners, airport authorities and commercial airlines on expanding the intensity of existing security requirements," it said.

"Due to the nature of the threat revealed by this investigation, we are prohibiting any liquids, including beverages, hair gels, and lotions from being carried on the airplane."

Travelers in the United States "should also anticipate additional security measures within the airport and at screening checkpoints," it added.

In response to the incident, Britain raised its 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.

British Airways (BA) said on Thursday that passengers 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 told passengers that no electrical or battery powered items including laptops and mobile phones could be allowed in the cabin.

Source: Xinhua