Venice is on a high state of alert following reports of a possible attack on the city's ancient Jewish ghetto by militants linked to the al-Qaeda network.

Officers from the specialist Digos anti-terrorist squad patrolled the ghetto area on Thursday and made checks around the synagogue and other buildings.

We are always alert in this area

Elia Richetti Chief Rabbi of Venice

Divers and small submarines were also checking canals in the area, reports said, but police would not say what they were looking for.

"There is an alarm in general, but I do not want to say anything more than that," Venice's Chief of Police, Domenico Bagnato, told the Ansa news agency.

He added: "For a few months now, there has been a general alert in Venice and more intensive security measures have been put into motion to avoid anything untoward taking place."

Elia Richetti, the Chief Rabbi of Venice, said they were helping police with the operation.

"There's no alarm, there's no panic whatsoever," he said. "We are always alert in this area."

Bomb plot

The web site of the Italian newspaper La Repubblica said that investigators had uncovered plans by a group linked to al-Qaeda to plant a bomb in Venice's Jewish area.

The newspaper's sources said the plot was one of three planned attacks that were "suspended" a few months before the 11 September attacks on New York and Washington.

On Wednesday, Milan daily newspaper Corriere della Sera carried a similar story, quoting a leaked report from the police's anti-terrorism unit.

It said that an Italian cell of the Algerian-based Salafist Group had been planning attacks on several targets last year including a church in Venice, St Peter's Square in Rome and US diplomatic missions in Europe.

Security in Rome has been tightened

But an order had been sent from London to halt the attacks, the newspaper said.

The report said that weapons and explosives were to be shipped from France or Pakistan.

It added that "similar logistical initiatives might be under way in Germany, France, Switzerland by cells deployed in the various states".

Corriere della Sera said that a suspect, believed to be the leader of the group, had been seen in Venice in May 2001 entering a church popular with Americans. The church was not named.

Italy has been on a high state of alert since the 11 September attacks.

In March, Italian police arrested eight Moroccans suspected of plotting a chemical attack on the US Embassy in Rome.

Milan, Venice, Florence and other Italian tourist destinations were also put on alert earlier this year following fears of possible attack during the Easter holy week celebrations.