Germany tightened its border security today to ensure that ten fugitive Islamic radicals suspected of helping three men arrested for plotting what would have been the worst terrorist attack in Germany could not flee the country.

The fugitives are believed to have given logistic support to the Islamic fundamentalists who were plotting to blow up hundreds of people in German airports, discotheques and pubs.”There are Germans, there are Turks, there are other nationalities,” said August Hanning, the deputy interior minister who is coordinating the hunt with the intelligence services.

Two of the fugitives are from Saarland close to the border with France. Most of the back-up team - who helped rent apartments, arrange cars and provided computer support - were based in western Germany within an easy drive of France, Switzerland and Belgium.

The core of the terror cell has however been destroyed, the police believe, with the arrest on Tuesday afternoon of two German Muslim converts and a Turk. All three were being questioned yesterday. ”There is no further danger from this terror cell, “ said Mr Hanning, a former head of the German security service and an acknowledged expert on terrorism. “ But there is still a mission to carry out attacks within Germany and this mission worries us.”

German politicians called today for the criminal prosecution of all Germans attending camps in northern Pakistan. The three arrested men - 28-year-old Fritz G, 22-year-old Daniel S and 29-year-old Adem Y - first met in a Taleban-linked camp in Pakistan where they learned explosives skills. When they returned to Germany they collected 750 kilos of hydrogen peroxide.

Correctly mixed and rigged up to detonators, the chemicals would have produced the explosive force of some 500 kilos of TNT - and produced a blast far bigger than the 7/ 7 London bombings.

”People who go to training camps like this are not after rest and recreation,“ said Ralf Stegner, interior minister of the region of Schleswig-Holstein. “They are being taught to be terrorists and that should be a criminal offence.” Mr Stegner is a Social Democrat but many senior Christian Democrats suggested similar action yesterday, indicating cross-party support for a quick crack-down.

Other calls came to monitor more carefully Germans who convert to Islam, since this is seen as a potential recruiting ground for radicals: the White Jihadists as they are becoming known. According to figures released yesterday 4000 Germans converted to Islam last year, compared to 1,000 in 2005.

The immediate concern of the police however is to capture the associates of the terror cell. “Above all we want to establish a chain of command and a precise organisational structure for the Islamic Jihad Union,” said a senior security service offical, referring to the shadowy Uzbekistan-based group behind the plot. The group has existed since 2004 and has been actively recruiting in the training camps. It is regarded as an affiliate of al-Qaeda and the technical detail of the plot, and the planned use of hydrogen peroxide, bears all the hallmarks of al-Qaeda. The chemical was the basis of the 7/7 London bombs and the failed bombs of 21/7.

Security sources said that there was "no significant connection" between the German plot and terrorist networks in Britain. They declined to comment on one newspaper report that the German suspects had made phone calls to Britain before their arrest.

Police calculate that there must be a direct communication link between the activists in Germany and the Islamic Jihad Union. “There must be a money paper trail,” said one investigator.

But despite monitoring conversations and e-mail traffic between Germany and Pakistan for nine months, the investigators seem to have discovered little. The search of 41 apartments immediately after the arrest of the terror cell has apparently produced some leads. But the key will be to find and interrogate the quartermaster of the group. The attack has been prepared for at least a year, entailing large expenses for the plotters.

”We cannot just rest on our laurels, “ said Joerg Ziercke, head of the Federal Criminal Intelligence Agency, the German equivalent of Scotland Yard. “We have to be particularly alert now.” The anniversary of the 9/11 attacks on the United States, which falls next week, is still regarded as potentially dangerous. Investigators have noted in the past that al Qaeda actions rarely take notice of anniversaries, in part because security is always so high.”But if converted Muslims are becoming an active force, they may think differently, be more Western in their assessment of what will grab media attention,” said one senior officer.

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