Hijacker 'planned to strike at US embassy'

· Airport gunman took flying lessons
· Police hunt four 'accomplices'

Security agencies across Europe are bracing themselves for a wave of terrorist attacks around the anniversary of 11 September after claims that the man arrested at a Swedish airport with a gun in his luggage was planning to hijack a London-bound plane and fly it into a US embassy somewhere in Europe.

British and Middle Eastern security officials say they believe that new details of the plot indicate it was a 'serious terrorist operation', not the work of a lone amateur, as thought at first.

Intelligence experts have been warning for months that Islamic militants, some linked to Osama bin Laden's al-Qaeda group, would try to pull off a series of spectacular attacks to demonstrate that they were still capable of major actions despite the year-long 'war on terror'.

Yesterday sources in the Swedish intelligence services said Kerim Chatty, 29, who was arrested last Thursday at Stockholm's Vastera airport as he tried to board a Ryanair flight to Stansted with the gun in a wash bag in his hand luggage, was part of a five-strong terrorist cell. He had undergone flight training in America, possibly as early as 1996. The cell was based in Sweden and planned to fly the plane into an embassy in an undisclosed European country, the Stockholm sources told Reuters news agency. The CIA confirmed the news, then denied having any information.

The claims sparked a fierce row in Sweden. Margareta Linderoth, director of the security police, denied her agency was looking for any more people and said she had no information that Chatty was aiming to fly the plane into an embassy. But some in Sapo, Sweden's security agency, said they had been instructed by the government to play down the incident at a politically sensitive time, two weeks before an election. There are fears anti-immigrant groups could try and exploit it.

The Swedish police did confirm that the suspect attended a flight school in Conway, South Carolina.

Chatty was said to have lived in a student flat in Conway between 1996-97 and paid $5,000 for a pilot training scheme. The fitness fanatic and kickboxer was carrying a 6.5 calibre pistol loaded with three or four rounds when he was arrested. His lawyer, Nils Uggla, said his client insisted the presence of the gun in his luggage could be explained. Chatty is in a high security prison and will probably be charged tomorrow with planning to hijack a plane, a police spokesman said.

Passengers on the plane, flown by the Irish budget airline Ryanair, included a group of 20 Muslims travelling to a conference in Birmingham on the future of the purist Salafi strand of Islam. Chatty appears to have been part of the group. Its organisers strongly condemned terrorism yesterday.

Swedish police have revealed that Chatty has previous convictions for theft and assault. He was jailed in 1998 for nine months for possessing a Glock machine pistol with 20 bullets. He has also served four months for an assault on a US embassy worker in Stockholm.

According to Aftonbladet, a Swedish newspaper, Chatty became a devout Muslim only in the past few years, regularly visiting a mosque in the Swedish capital. His friends told the paper he often spoke of fighting for Islam but was not a member of any organisation.

Sapo had been monitoring his movements and he was questioned after last year's terrorist attacks. A friend told the newspaper: 'He wanted to be part of jihad [holy war].'

Swedish police said they found literature at his flat linking him to extremist organisations, but no clear link to al-Qaeda or any other militant group has emerged. Experts say an affiliation with Salafi Islam does not necessarily indicate support for al-Qaeda and its methods.

British security agencies are on high alert. A Scotland Yard spokesman said British police were 'liaising as a matter of course with Swedish authorities and continue to offer every assistance. This may involve sending anti-terrorist officers in due course.'

A Home Office spokesman refused to comment on reports of the terror cell, but said: 'Airport security is already operating at increased levels and this is a timely reminder of the need for vigilance.'

Several previous bomb attempts linked to al-Qaeda have involved recent converts to Islam with histories of crime or drug abuse. Nisar Trabelsi, linked to a British-based cell created by al-Qaeda recruiter Djamal Beghal, was a drug user.

Richard Reid, the 'shoe bomber' who tried to blow up a transatlantic jet in December, had convictions for shoplifting. Jerome Padilla, in custody in America, was a former gang member who converted to Islam from Catholicism while in prison.

Security experts say al-Qaeda recruiters target young and vulnerable Muslims who gather at mosques in the West.

An older man, often a veteran of Afghan training camps, might travel to Europe or elsewhere to recruit and motivate a group of younger men to commit terrorist attacks. He helps arrange logistical support and then disappears.