US experts join 'terror tunnel' probe

Officials from Washington are in Rome to inspect a tunnel which Italian investigators suspect may have featured in a plan to launch a chemical attack against the US embassy.

At this stage there is a lot of circumstantial evidence

US embassy official

Rome has been under a heightened alert in the past week following the detention of four Moroccans found with large quantities of a cyanide-based compound and maps of the water network surrounding the embassy. A total of nine Moroccans are now being held.

Security was stepped up even further on Tuesday morning following a minor bomb blast near the Interior Ministry, the motive for which remains unclear.

The US mission was due to examine a utility tunnel running alongside the embassy. Following the arrests last week, a hole was discovered in the tunnel wall, just a few metres away from one of the building's water supply points.

Workmen

Officials stress that evidence suggesting the men were planning some kind of attack is circumstantial and that the hole may have been created by workmen carrying out standard utility maintenance.

But the hole is not thought to have been there when authorised work was last carried out on 15 January.

Scientists have pointed out that the compound found in the Moroccans' flat, potassium ferrocyanide, is a harmless substance in itself.

It can be turned into a gas capable of killing people, but this would involve a complicated process. US embassy officials indicated on Tuesday morning that carrying out a chemical attack on the embassy would have posed enormous difficulties.

"Most of our experts seem to believe that, at this stage anyway, it would have been extremely difficult for them to do this," one official told reporters.

Tunisians jailed

Following last week's arrests of the Moroccans, police said they had evidence from telephone bugging linking some of the men to four Tunisians jailed last week after being accused of al-Qaeda links.

The four Tunisians were convicted of conspiring to traffic in false documents, weapons, explosives and chemical weapons.

Police believe that one of the men, Essid Sami Ben Khemais, was himself planning an attack on the US Embassy in Rome in January last year.

They also believe he was a key European operative for Osama Bin Laden.

'Internal subversion'

As inquiries continue into Tuesday's bomb blast, anti-terrorist prosecutors said they believed it was more likely to be linked to "internal" subversion than international terrorism.

It is thought the bomb was attached to a scooter

It is believed that an explosive was attached to a scooter on a pavement near the ministry. It blew up in the early hours of the morning, damaging several vehicles and blowing out the windows of nearby flats.

Police are interviewing a Dutch eyewitness staying in a hotel near the ministry, who said he saw three young men leave the scene just after the blast occurred.

The country has weathered a spate of explosions in the past of 18 months carried out by domestic extremist groups.

In August last year a left-wing "anti-imperialist" faction claimed responsibility for a bomb blast at a Venice courthouse a day before Prime Minister Silvio Berlusconi was due to visit. Other small explosions have hit Milan, Trieste and Bologna.