London ? Explosions struck the London Underground and a bus at midday today in a chilling but far less bloody replay of the suicide bombings that killed 56 people two weeks ago.

Only one person was reported injured in the nearly simultaneous lunch-hour blasts, British Transport Police said, but they caused major shock and disruption in the capital and were hauntingly similar to the July 7 bombings by four attackers.

Panicked and screaming commuters fled the three affected Underground stations, sometimes leaving behind their shoes. Firefighters and police with bomb-sniffing dogs sealed off nearby city blocks and evacuated rows of restaurants, pubs and offices.

Prime Minister Tony Blair appealed for calm and said it was too early to tell who was responsible.

“We can’t minimize incidents such as this,” he said at a joint news conference with the Australian prime minister at No. 10 Downing St. “They’re done to scare people, to frighten them and make them worried.”

He held an emergency Cabinet meeting afterward but said no decisions “of a policy nature” were made.

Metropolitan Police Commissioner Ian Blair called it “a very serious incident.”

“We know that we have four explosions or attempts of explosions, and it is still pretty unclear as to what has happened,” he said outside Scotland Yard.

“At the moment the casualty numbers appear to be very low … the bombs appear to be smaller” than those detonated July 7, he said.

An armed police unit entered University College hospital shortly after an injured person was carried in, Britain’s Press Association reported.

Sky News TV reported that police were searching for a man with a blue shirt with wires protruding. Officers asked employees to look for a black or Asian male about 6-foot-2.

The attacks, which targeted trains near the Warren Street, Oval and Shepherd’s Bush stations, did not shut down the subway system, only three of its lines. The double-decker bus had its windows blown out on Hackney Road in east London.

Witnesses told The Associated Press they did not hear a bang but smelled something similar to an electrical fire at the Warren Street station.

Police in chemical protection suits were at the Warren Street station, but no chemical agents were found.

Stagecoach, the company which operates the stricken bus, said the driver heard a bang and went upstairs, where he found the windows blown out. The company said the bus was structurally intact and there were no injuries.

The incidents paralleled the July 7 blasts, which involved explosions at three Underground stations simultaneously starting at 8:51 a.m., followed quickly by a bomb going off on a bus. Those bombings, during the morning rush hour, also occurred in the center of London, hitting the Underground from various directions.

Thursday’s incidents, however, were more spread out.

Emergency teams were sent to all three stations after the incidents, which began at 12:38 p.m.

“People were panicking. But very fortunately the train was only 15 seconds from the station,” witness Ivan McCracken told Sky news.

McCracken said another passenger at Warren Street told him he saw a backpack explode. The July 7 bombs were carried in backpacks, police said.

McCracken said he smelled smoke, and people were panicking and coming into his carriage. He said he spoke to an Italian man who was comforting a woman after the evacuation.

“He said that a man was carrying a rucksack and the rucksack suddenly exploded. It was a minor explosion but enough to blow open the rucksack,” McCracken said. “The man then made an exclamation as if something had gone wrong. At that point everyone rushed from the carriage.”

Losiane Mohellavi, 35, who was evacuated at Warren Street, said, “I was in the carriage and we smelled smoke – it was like something was burning. Everyone was panicked and people were screaming. We had to pull the alarm. I am still shaking.”

The U.S. Embassy was closed to visitors about two hours after the blasts as a precaution, but embassy staff continued working, said spokeswoman Susan Domowitz.

The explosions came as Pakistani intelligence officials said authorities are seeking the former aide of a radical cleric in Britain in connection with the July 7 bombings.

The officials said British investigators asked Pakistani authorities to search for Haroon Rashid Aswat, who reportedly had been in close contact with the suicide bombers just before the July 7 attacks.

Aswat, 31, was of Indian origin and may not be in Pakistan, according to two intelligence officials in Islamabad and one in Lahore, all speaking on condition of anonymity because they are not authorized to talk to the media and because of the sensitivity of the investigation.

Aswat reportedly was once an associate of Abu Hamza al-Masri, the radical imam who is awaiting trial in Britain on charges of incitement to murder. Al-Masri also is wanted in the United States on charges of trying to establish a terrorist training camp in Bly, Ore.; involvement in hostage-taking in Yemen; and funding terror training in Afghanistan.

Quoting unidentified intelligence sources, The Times of London said Aswat visited the hometowns of all four London bombers and selected their targets. It also reported there had been up to 20 phone calls between Aswat and two of the bombers in the days before the attacks.

Aswat’s relatives in Batley, near the northern English town of Leeds, which was home to two of the July 7 suicide bombers, said they had not heard from him for many years.

“He has not lived at this house and we have not had contact with him for many years,” said his father, Rashid, who asked for his family to be left in peace. “There is no story that we can provide.”

Authorities are investigating whether the London bombing suspects, three of whom were of Pakistani origin and traveled to Pakistan last year, received training or other assistance from militants in that country.

One of the July 7 bombers, Shahzad Tanweer, 22, is suspected of visiting a madrassa linked with militants in Lahore which has become a focus of the inquiry.

According to a report in a Pakistani newspaper, Tanweer revered Osama bin Laden. The English-language Dawn newspaper said Tanweer visited relatives in November in a farming village near Faisalabad in eastern Pakistan. During his weekslong stay, he was visited by another suicide bombing suspect, Mohammed Sidique Khan, 30, Tanweer’s uncle told the newspaper.

Pakistan has pledged to curb religious extremism amid international concerns that Islamic schools, or madrassas, are promoting extremism.

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Associated Press reporters Thin Lei Win and Kate Bouey in London and Christopher Torchia in Islamabad, Pakistan, contributed to this report.