An attack by an al-Qaeda terrorist commando... might have been just days away, or even hours away

Investigators

Photos of the holes - large enough for a person to get through - have been forwarded to prosecutors handling the case of Moroccan men arrested with suspected bomb-making equipment last week.

The Moroccans were found with large quantities of a cyanide compound, explosive powder and maps of the water network around the US embassy on Via Veneto in the heart of Rome.

After the arrests, police and maintenance staff checked tunnels around the embassy complex that carry water, gas and electricity to buildings in the area, and found a hole cut into a wall next to the diplomatic mission.

The hole was not there when authorised work was last carried out on 15 January.

The Corriere della Sera newspaper reported that investigators also discovered a ladder and workman's uniform that was different from the type used by utility workers.

"An attack by an al-Qaeda terrorist commando on the American embassy might have been just days away, or even hours away," the leading daily quoted investigators as saying.

Scientists said the chemical compound found in the Moroccans' apartment - potassium ferrocyanide - was harmless in itself but could have been turned into a gas capable of killing large numbers of people.

Gas blast

A police explosives expert said there could have been many deaths if the substance had exploded under the embassy.

"A toxic cloud would have formed and spread through the tunnels under the centre of Rome," the expert told Rome's Il Messaggero newspaper.

"They might have reached the air-conditioning units of the embassy and other buildings."

FBI agents are in Rome to work with the Italian police

The expert, who declined to be named, said a bomb might also have triggered a gas explosion.

Judicial sources say nine Moroccans are now in custody in connection with the cyanide haul and are under investigation for planning terrorist attacks.

Agents from the US Federal Bureau of Investigation have arrived in Rome to work with the Italians.

A judge is to rule on Sunday whether the Moroccans can continue to be detained.