An official briefed on the attack on a Detroit airliner said Saturday the US has known for at least two years that the suspect in the attack could have terrorist ties. The official told The Associated Press that the suspect, Umar Farouk Abdul Mutallab, has been on a list that includes people with known or suspected contact or ties to a terrorist or terrorist organization. The official spoke on condition of anonymity because the investigation is ongoing. The Terrorist Identities Datamart Environment list is maintained by the US National Counterterrorism Center. It includes about 550,000 names. People on that list are not necessarily on the no-fly list, and Mutallab reportedly was not. Police searched a London apartment Saturday as authorities probed the background of a Nigerian man who attempted to down a Northwest Airlines jetliner. A prestigious London university said Saturday that a man with a similar name had studied mechanical engineering at the school for three years. University College London said a man called Umar Farouk Abdulm Mutallab was enrolled at the school from September 2005 to June 2008. In Nigeria, the father of Umar Farouk Abdul Mutallab - identified by US officials as the man who set a fire on a Detroit-bound jetliner - said his son had been a student in London, but had left the city to travel. Mutallab is accused of trying to destroy Northwest Airlines Flight 253, which was minutes away from touching down in Detroit after leaving Amsterdam earlier on Christmas Day. Home Secretary Alan Johnson called the thwarted attack a "potentially serious security threat" and said British investigators were working with their American counterparts. Prime Minister Gordon Brown said he had spoken with the head of London's Metropolitan Police about the incident. University College London, which was ranked as the world's No. 4 university earlier this year by US News and World Report, said that while they could say that a student with a very similar name had attended the school, "it must be stressed that the university has no evidence that this is the same person currently being referred to in the media." Officers from the Metropolitan Police - the force is involved in most of the major terrorism investigations in Britain - went in and out of an imposing white stone apartment block in a well-to-do area of central London. A police spokeswoman said the force was carrying out searches in connection with the incident in Detroit, but would not say if the searches at the building were connected. The seven-story building is a stone's throw from London's busy Oxford Street shopping area. It was adorned with ornate carvings on its facade and antique lamps flank an imposing front door. Officers searching the residence wore regular uniforms. On past searches of terror suspects' houses, officers have worn protective clothing. In Nigeria, a prominent banker said Saturday that he was meeting with security officials there because he feared his son was the suspect. Alhaji Umaru Mutallab told The Associated Press that his son was a one-time university student in London who had left Britain to travel abroad. He said his son hadn't lived in London "for some time" but he wasn't sure exactly where he went to. "I believe he might have been to Yemen, but we are investigating to determine that," the elder Mutallab said. He said he would provide more details later Saturday as he learned more from authorities. The attempted terrorist attack on a Christmas Day flight began with a pop and a puff of smoke - sending passengers scrambling to tackle a Nigerian man who claimed to be acting on orders from al-Qaida to blow up the airliner, officials and travelers said. The commotion began as Northwest Airlines Flight 253, carrying 278 passengers and 11 crew members from Amsterdam, prepared to land in Detroit just before noon Friday. Travelers said they smelled smoke, saw a glow, and heard what sounded like firecrackers. At least one person climbed over others and jumped on the man, who officials say was trying to ignite an explosive device. "It sounded like a firecracker in a pillowcase," said Peter Smith, a passenger from the Netherlands. "First there was a pop, and then [there] was smoke." Smith said one passenger, sitting opposite the man, climbed over passengers, went across the aisle and tried to restrain the man. The heroic passenger appeared to have been burned. Afterward, the suspect was taken to a front-row seat with his pants cut off and his legs burned. Multiple law enforcement officials also said the man appeared badly burned on his legs, indicating the explosive was strapped there. The components were apparently mixed in-flight and included a powdery substance, multiple law enforcement and counterterrorism officials said. The White House said it believed it was an attempted act of terrorism and stricter security measures were quickly imposed on airline travel. Dutch anti-terrorism authorities said the US has asked all airlines to take extra precautions on flights worldwide that are bound for the United States. The incident was reminiscent of Richard Reid, who tried to destroy a trans-Atlantic flight in 2001 with explosives hidden in his shoes, but was subdued by other passengers. Reid is serving a life sentence. One law enforcement official said the man claimed to have been instructed by al-Qaida to detonate the plane over US soil, but other law enforcement officials cautioned that such claims could not be verified immediately, and said the man may have been acting independently - inspired but not specifically trained or ordered by terror groups. All the officials spoke on condition of anonymity because the investigation was continuing. Intelligence and anti-terrorism officials in Yemen said they were investigating claims by the suspect that he picked up the explosive device and instructions on how to use it in that country. The officials spoke on condition of anonymity because they are not authorized to speak to the media. Melinda Dennis, who was seated in the front row of the plane, said the man involved was brought to the front row and seated near her. She said his legs appeared to be badly burned and his pants were cut off. She said he was taken off the plane handcuffed to a stretcher. An intelligence official said he was being held and treated in an Ann Arbor, Michigan, hospital. The hospital said one passenger from the flight was taken to the University of Michigan Medical Center in Ann Arbor, but referred all inquiries to the FBI. One law enforcement official, also speaking on condition of anonymity, said Mutallab's name had surfaced earlier on at least one US intelligence database, but he was not on a watch list or a no-fly list. The suspect boarded in Nigeria and went through Amsterdam en route to Detroit, Rep. Peter King, the ranking Republican member of the House Homeland Security Committee, told CNN. A spokeswoman for police at the Schiphol airport in Amsterdam declined comment about the case or about security procedures at the airport for Flight 253. Dutch airline KLM says the connection in Amsterdam from Lagos, Nigeria, to Detroit involves a change in carrier and a change in aircraft. Dutch antiterrorism authorities said Saturday that Mutallab was traveling on a US visa valid through the first half of 2010. She said an initial investigation showed that routine security procedures were followed at Schiphol airport with no irregularities. Mutallab's name was on the passenger manifesto that was forwarded and approved by US authorities before takeoff. Nigeria's information minister, Dora Akunyili, condemned the attempted bombing. She said the government has opened its own investigation into the suspect and will work with US authorities. "We state very clearly that as a nation we abhor all forms of violence," Akunyili said in a statement issued Saturday. Delta Air Lines Inc., which acquired Northwest last year, said a passenger caused a disturbance, was subdued, and the crew requested that law enforcement officials meet the flight. Passenger Syed Jafry, a US citizen who had flown from the United Arab Emirates, said the incident occurred during the plane's descent. Jafry said he was seated three rows behind the passenger and said he saw a glow, and noticed a smoke smell. It was another passenger, who Jafry described as being in his 20s or early 30s and having a medium, stocky build, who quickly jumped toward the man who had started the fire. "He did a good job with his power, tackled him and put him under arrest," Jafry said Saturday. Federal officials said there would be heightened security for both domestic and international flights at airports across the country, but the intensified levels would likely be "layered," differing from location to location depending on alerts, security concerns and other factors. Passengers can expect to see more screening, bomb-sniffing dogs, officer units and behavioral-detection specialists at some airports, but there will also be unspecified less visible precautions as well, officials said. The FBI and the Homeland Security Department issued an intelligence note on Nov. 20 about the threat picture for the holiday season, which was obtained by The Associated Press. At the time, officials said they had no specific information about attack plans by al-Qaida or other terrorist groups. President Barack Obama was notified of the incident and discussed it with security officials, the White House said. Officials said he is monitoring the situation and receiving regular updates from his vacation spot in Hawaii.