Terrorist threat remains 'very substantial,' Britain warns

Four days after two dozen people were arrested under British anti-terrorism laws and accused of plotting to bomb airplanes, Home Secretary John Reid is warning: "There could be others out there."

Airports in Britain, Canada, the United States and elsewhere boosted security after police in London announced the arrests on Aug. 10, alleging that the suspects had been within days of trying to blow up as many as 10 commercial flights.

On Sunday, Reid said that while a major plot had been foiled, the threat of others remains.

"I have to be honest to say that, on the basis of what we know, there could be others out there, perhaps people we don't know, perhaps people who are involved in other plots," he said in an interview with the BBC.

"So the threat of a terrorist attack in the United Kingdom is still very substantial."

Flight delays, cancellations continue

Britain remained on the highest possible level of terrorist alert on Sunday, and Reid said he believed the decision was the right one.

He said police and security forces were working hard to protect the public, but warned: "We can never guarantee 100-per-cent success."

In the aftermath of the arrests, Britain's air services continued to move slower than normal. At London's busy Heathrow airport on Sunday, about one-third of the flights were cancelled.

Officials blamed stringent new screening rules imposed on Aug. 10, which include a ban on all carry-on luggage.

4 major plots uncovered in year: Reid

The home secretary said at least four major plots had been uncovered since the July 7, 2005, attacks on the London transit system that killed 56 people, including the suicide bombers.

In the latest alleged plot, authorities have accused the suspects of planning to smuggle explosives onto about 10 transatlantic flights and blow up them up in mid-air.

The suspects are said to be British nationals with links to Pakistan. The Bank of England released the names of 19 suspects on Friday and said that their assets had been frozen.

Brothers accused of leading plot

On Saturday, officials in Pakistan said two brothers arrested in that country and in Britain have emerged as lead figures in the investigation of the alleged plot.

Rashid Rauf, who was arrested along the border between Pakistan and Afghanistan about a week ago, has been listed as a "key person" in the investigation, authorities with Pakistan's Foreign Ministry said.

Rauf's brother, Tayib Rauf, 22, was arrested in Britain. Police there have refused to comment on reports that a third brother is among the 40 people who have been detained in the two countries.