There has been an arrest, but I think it is in the interests of the inquiry not to reveal any details

Otto Schily, German Interior Minister

Returning from a two-day visit to Tunisia, Minister Otto Schily told ZDF television that inquiries were continuing in other countries, including Canada, France and Pakistan.

Mr Schily said it was believed two people in Tunisia were involved in the incident, but added it was "in the interests of inquiry not to reveal any details".

Tunis had initially said the explosion was an accident, but on Monday an official statement said the driver of the fuel lorry was responsible.

It was "a premeditated crime perpetrated by a Tunisian, Nizar Ben Mohamed Nasr Nawar, with the aid of one of his relatives resident in Tunisia," the statement read.

Nawar, a 24-year-old resident of the French city of Lyon, is believed to have died in the blast.

'Al-Qaeda link'

According to the Tunisian statement Nawar acted "in complicity with one of his close relatives living in Tunisian".

Mr Schily said he learned some "extremely interesting details" during his meeting on Monday with Tunisian President Zine al-Abidine Ben Ali.

Most of those affected were German tourists

The nature of the explosion, the type of fuel and the way the tanks were mounted on the lorry had all combined to convince investigators that the attack was deliberate, he said.

German ministers have said there is evidence that al-Qaeda was behind the attack, but Mr Schily said it was too soon to link it Osama Bin Laden's terrorist network.

"For the time being, we can't say it was al-Qaeda," he said.

The London-based Arab newspaper, al-Quds al-Arabi, has published a letter purporting to be from al-Qaeda, saying it had attacked the synagogue.

The writer's name matches that of the truck's driver.