By Rob Broomby The BBC's Berlin correspondent

The German authorities are investigating newspaper reports that members of the Taleban and al-Qaeda have been smuggled into Europe to plan new attacks, possibly in Britain, according to the German interior minister.

Otto Schily said that officials are investigating reports in the Frankfurter Allgemeine newspaper that 30 Taleban and al-Qaeda members had disappeared in Slovakia.

But he said there were no concrete indications of an imminent attack.

Mr Schily was speaking at the publication of the annual report on extremism by the federal office for the protection of the constitution of Germany.

Extremist threat

The newspaper suggested that the extremists may have been heading for Britain to regroup.

The West has been on the alert since the US attacks

Mr Schily confirmed that the authorities had received a report in that direction, and were following it up.

The newspaper report cited a warning letter from Interpol to law enforcement officers and border guards.

It suggested that the group had fled a refugee camp in Slovakia on 12 March and had not been seen since.

The group was claiming asylum in the country, having been smuggled through Bulgaria and Hungary, it said.

Mr Schily described Islamic extremism as the greatest threat to German internal security.

But he warned of what he called "alarmism", saying great efforts were needed to confront the danger without giving way to panic.

New figures show a marginal increase in the membership of what were considered to be foreign extremist organisations - 59,000 members of such groups have been counted.

Germany has been under the spotlight since it emerged that the 11 September attacks were partly planned on German soil.