They were all arrested in raids in London and other British cities and towns a week ago. Under anti-terrorist laws, they can all be held without charge for no more than 28 days, subject to regular court approval.

Few details have been released about the alleged plot, but it appears that the plot involved suicide bombers smuggling liquid explosive disguised as drinks on to US airliners, then detonating them with electronic devices in mid-air.

Meanwhile, British Home Secretary John Reid warned Wednesday that Europe as a whole is facing a "very real" and "persistent" risk of a devastating attack, in a meeting with
European Union interior ministers in London to map out a common strategy.

"What's clear to all of us is that we face a persistent and very real threat across Europe," said Reid after the talks, at which the European Commission promised to introduce a series of measures to strengthen airport security, boost cross-border intelligence sharing and tighten controls on explosives.

Those taking part in Wednesday's talks in London included the French and German interior ministers, Nicolas Sarkozy and Wolfgang Schaeuble, as well as Kari Rajamaki from Finland, which holds the rotating EU presidency.

European Commission Vice President Franco Frattini, who was also present, said Brussels would draft new measures to enhance airport security and cross-border cooperation before the Finnish presidency ends in December.

He suggested steps to encourage what he called "a European Islam", including the training of imams, and the blocking of Internet websites deemed to be inciting terrorism.

Frattini also said the European Commission -- the executive arm of the 25-nation EU -- would be bringing forward new proposals in the coming days relating to controls on liquid explosives and commercial detonators.

European ministers also released 350,000 euros (450,000 dollars) for urgent research into technology for detecting liquid explosives following Wednesday's meeting, a Home Office spokeswoman told AFP.

Sarkozy, the French interior minister and likely presidential candidate, meanwhile said there was "a pile of elements that make one think that the Al-Qaeda connection is not far removed from what could have happened."

Reid and Sarkozy on Wednesday signed a text pledging cooperation between their countries in the fight against terrorist activity in Europe.

The threat of terrorism is "heightened and permanent" said the French text of the agreement, a copy of which was obtained by AFP ahead of publication in French daily Le Figaro.

They agreed their efforts should aim to prevent terror attacks and protect the public, as well as pursue and arrest terrorists, following the talks in London.

In Islamabad, officials said Pakistan was holding a man who is "apparently related" to one of the British suspects, and that a senior Al-Qaeda figure in
Afghanistan is thought to have planned the foiled attacks.

Reid refused to confirm or deny if Britain was seeking the extradition of suspects -- two British and five Pakistani -- from Pakistan, but he expressed his "gratitude" to Islamabad for its role in the investigation.

Security worries escalated later Wednesday on news that a United Airlines flight from London to Washington was diverted to Boston, and its passengers and baggage searched, because of what officials called an "unruly" traveller on board, though the incident did not seem to be related to terrorism.

London's main Heathrow airport, the busiest international airport in the world, and other facilities were running almost normally again Wednesday, after prolonged chaos and disruption.

However, British Airways cancelled 35 flights at Heathrow and 11 at Gatwick -- and it also emerged that 20,000 pieces of baggage have gone astray at Heathrow over the past seven days.

According to The Times on Tuesday, the Department for Transport was considering a system to single out people behaving suspiciously, who have an unusual travel pattern, or a certain ethnic or religious background.

But the plan -- similar to a system operated by Israeli airline El Al -- was immediately condemned by one of Britain's most senior Muslim police officers, who said that could lead to a new offence of "travelling whilst Asian".

The debate was sparked after British police and intelligence services staged pre-dawn raids on the homes of 24 people, the majority of whom appear to be British Muslims, to disrupt what they believed was a plot to blow up US-bound passenger jets in mid-flight.

Half of the respondents said they thought most British Muslims were moderates, but more than a quarter disagreed.

Only 12 percent of those surveyed said they thought Britain's foreign policy should be made more conciliatory in response to terrorism.

By contrast, 80 percent of those polled wanted British Prime Minister Tony Blair to distance himself from US President George W. Bush and either work more closely with European countries or blaze his own path.

Blair was heavily criticised in Britain during the conflict between Israel and the Shiite militia Hezbollah over the past month as he sided with the US president in declining to call for an immediate ceasefire.

Some 69 percent of those surveyed also felt that police should be allowed to hold suspects in anti-terrorism investigations for 90 days, as opposed to the 28 days allowed under current legislation.

Shooting down hijacked passenger planes could be justified if the threat to Germany was considered severe, Schaeuble said, according to the paper. "In the case of Sept. 11, the shooting down (of the hijacked planes) would have been necessary as well as legally admissible," he was quoted as saying.

The Federal Constitutional Court struck down the 2005 air safety law in March, saying authorities had no right to kill innocent civilians. It also found that allowing the military to shoot down civilian airliners violates a constitutional bar on the military being deployed for domestic security.

With reference to the latest alleged plot to blow up passenger planes taking off from Britain, Schaeuble said Germany also faces a growing threat from suicide attackers, according to the report.

"We must recognize that there are also here more such people than we can imagine who are ready to sacrifice their own lives in madness or as fanatics," he was quoted as saying.

Also Wednesday, the Interior Ministry said officials will next week begin finalizing plans for a national database on terror suspects, despite a dispute over whether individuals' religious affiliation should be included.