UK police on Saturday were given a further four days to question 22 suspects arrested followed the discovery of a plot to blow up as many as 10 passenger airplanes over the Atlantic. The arrests were made during police raids in London, Birmingham and High Wycombe in Buckinghamshire Thursday. The suspects allegedly planned to detonate liquid explosives smuggled on board in hand luggage on flights from the UK to the US. Materials thought to be for bomb-making were found in at least one of the raids. Computer equipment was also seized from three Internet caf s in Berkshire on Saturday morning. One of the 24 people arrested has been released without charge and the hearing of another has been adjourned until Monday. The Bank of England has frozen assets of 19 of the suspects, all said to be Muslims of British and Pakistani origin. Three are said to be recent converts to Islam. Details of the plot came from intelligence supplied by authorities in Pakistan, where seven people have been arrested in Karachi and Lahore, including two British nationals. Pakistani authorities have identified British citizen Rashid Rauf as one of the seven, saying he is the brother of Tayib Rauf, 22, one of those held in Britain. They also claim that Rashid Rauf has ties to al-Qaida. It has also emerged that an intercepted telephone call from Pakistan to Britain may have played a pivotal role in the discovery of the plot. A senior Pakistani security official said the arrest of Rashid Rauf was followed within days by a telephone call from someone in Pakistan urging the British plotters to execute their plan. "This telephone call intercept in Karachi and the arrest of Rashid Rauf helped a lot to foil the terror plan," said the official. The Pakistani said that most of those linked to the plot in Pakistan had been arrested. Among the two or three still at large, he said, was Matiur Rahman, a senior figure in the al-Qaida-linked Pakistani terrorist group, Lashkar-e-Jhangvi, whose name was mentioned by one of the detainees during interrogation. Rahman is wanted in Pakistan in connection with attacks on minority Shi'ites, two failed attempts on the life of Pakistani President Gen. Pervez Musharraf in December 2003, and attacks in Karachi against Westerners, the official said. Rahman is believed to have met with some al-Qaida operatives in recent years, he added. In Texas, US President George Bush said Saturday authorities cannot be certain arrests made in the terror scheme to blow up several flights between Britain and the United States have eliminated the plan's threat, justifying the dramatic increase in security at US airports. "We believe that this week's arrests have significantly disrupted the threat," Bush said in his weekly radio address, taped Friday at his Texas ranch. "Yet we cannot be sure that the threat has been eliminated." Bush said the terror plot was carefully planned, welladvanced and had the potential to cause "death on a massive scale." He also said it was a stark reminder that terrorists still aim to kill Americans five years after the September 11 attacks. Bush authorized an increase in the terror threat warning for flights on that route to code red, indicating a severe risk of terror attacks. All other domestic and international flights in the US were set to code orange, the second highest level on the scale. The terror plot called for the attackers to assemble their bombs aboard the aircraft, apparently with a peroxide-based solution disguised as beverages or other harmless-seeming items, and using such electronic equipment as a disposable camera or a music player as a detonator, two US law enforcement officials said. A US intelligence official said they planned to deploy a couple of attackers per plane. The British said their inquiry began months ago - prompted by a tip from within the British Muslim community after the bloody July 7, 2005, terror bombings of the London transit system, The Washington Post reported. Police said Saturday they were investigating whether a fire at a mosque in southern England was set in revenge for the aircraft plot. The fire was reported early Saturday at the al-Birr Masjid Mosque in Basingstoke, 80 kilometers southwest of London. Fire crews extinguished the fire within two hours. Meanwhile, British Muslim leaders have written to Prime Minister Tony Blair calling for "urgent changes to British foreign policy." The open letter, which appeared as a full-page advertisement in some of Saturday's British newspapers, was signed by 38 Muslim groups, three Muslim members of Parliament and three members of the House of Lords. The letter, citing Iraq and the crises in Lebanon and the Gaza Strip, blames British foreign policy as the root cause of extremism among some British Muslims. According to the letter, the "debacle" of Iraq combined with the recent failure to do more to bring about an immediate end to attacks on civilians in the Middle East, not only increased the risk to people there but also fuelled extremists who threatened people in Britain. It also says that attacks on civilians are never justified and calls on Blair to "show the world that we value the lives of civilians wherever they live and whatever their religion." Labor MP Sadiq Khan, who signed the letter, said that British foreign policy was seen by Muslims as "unfair and unjust." A spokesman for Blair responded to the letter by saying, "We should always remember that the terrorism affecting the West today has blighted Muslim countries for several decades. "It certainly predated our decision to support democracy in Afghanistan and Iraq and of course the September 11 attacks. Our foreign policy is focused on supporting the people of those countries in their desire to live in a democracy just as we enjoy in the UK." Blair, who is currently on holiday, called Pakistan President Musharraf to thank him for his country's role in thwarting the potential attack. Security in the UK remained at "critical" on Saturday, the highest level of alert, and travelers at British airports faced long delays, canceled flights and stringent security. Tony Douglas, chief executive of the British Airport Authority, said the restrictions "would remain in force for some time". British Home Secretary John Reid said on Saturday that the arrests did not diminish the current terror threat. "This is not a time for complacency or self-congratulation. As I have said all along, no one should be under any illusion that the threat ended with the recent arrests. The threat, as well as our efforts, is ongoing," he said. London's Heathrow airport canceled one-third of flights due out Saturday afternoon and night, blaming strict new security regulations for problems that caused passengers to miss flights. "Whilst the need for this action is extremely regrettable, it is the only way that services at Heathrow can continue to return to normal operations," said BAA PLC, the owner of Europe's busiest airport. British Airways said it had canceled one-quarter of its regional flights from Heathrow and accused the airport owner of failing to cope with the problems posed by strict new security regulations. AP contributed to this report.