Italian Interior Minister Giuseppe Pisanu said in a statement on Friday: "The arrest took place a short while ago in Rome of the Somalian, Osman Hussain, a naturalised British citizen.
"The anti-terrorism operation is still ongoing, and has been conducted in the context of close international collaboration."
He gave no details of the arrest.
Earlier on Friday London's Metropolitan Police confirmed the arrest of three men during two raids in the west of the capital, while refusing to confirm that among them were suspected bombers who targeted the city last week.
"Police have arrested two men at one address and a third man has been arrested at the second address. They are being taken to a central London police station for further questioning," a police statement said on Friday.
The police, however, said that Friday's arrests were connected to the failed July 21 attacks on London's transport network.
British broadcast media earlier reported that at least two of the three men being sought for the failed bombings had been arrested.
Armed police also arrested two women at Liverpool Street station, located in central London, and evacuated the area.
British Transport Police (BTP) said the operation was carried out by the Metropolitan Police and confirmed that the site was being searched.
Both the mainline station and its Underground station were evacuated.
"The two women were arrested at around 1.54pm (1254 GMT) and the station is now closed. The Tube is passing through on a non-stop basis," a BTP spokesman said on condition of anonymity in accordance with British practice.
The 21 July attacks targeted three undergound trains and a bus, but there were no victims and police said the explosive devices failed to detonate properly.
Police have been under pressure to exercise caution after they shot dead Brazilian Jean Charles de Menezes in London last Friday because they mistook him for a bomber.
British police arrested the three
men after raids in west London
London's Metropolitan Police Commissioner Ian Blair said he was devastated for the man's family but defended the shoot-to-kill policy with bombers.
In the biggest manhunt ever undertaken by British police, Blair said he was confident the three would-be bombers on the run would be caught.
"How soon it will be, I don't know. But I am quite sure the net is closing," he said.
Police are reviewing 15,000 closed-circuit television tapes, have taken 1800 witness statements and received 5000 calls on their anti-terrorism hotline.