The allegation was made by General Gianadelio Maletti, a former head of military counter-intelligence, at the trial last week of rightwing extremists accused of killing 16 people in the bombing of a Milan bank in 1969 - the first time such a charge has been made in a court of law by a senior Italian intelligence figure.

Gen Maletti, comannder of the counter-intelligence section of the military intelligence service from 1971 to 1975, said his men had discovered that a rightwing terrorist cell in the Venice region had been supplied with military explosives from Germany.

Those explosives may have been obtained with the help of members of the US intelligence community, an indication that the Americans had gone beyond the infiltration and monitoring of extremist groups to instigating acts of violence, he said.

"The CIA [Central Intelligence Agency], following the directives of its government, wanted to create an Italian nationalism capable of halting what it saw as a slide to the left and, for this purpose, it may have made use of rightwing terrorism," Gen Maletti told the Milan court. "I believe this is what happened in other countries as well."

The general has been living in South Africa for the last 21 years as a fugitive from Italian justice. He has been sentenced to 14 years imprisonment for leaking a secret service document to the press and last year received a 15-year sentence for obstructing justice. He was granted a special 15-day immunity from arrest to enable him to give evidence at the trial for the bombing of a bank in Milan's Piazza Fontana, the atrocity that inaugurated the "strategy of tension", a series of bombings intended to shift the country's political centre of gravity to the right.

"The impression was that the Americans would do anything to stop Italy from sliding to the left," Gen Maletti said during an interview at his Milan hotel.

"Don't forget that [former US president Richard] Nixon was in charge and Nixon was a strange man, a very intelligent politician but a man of rather unorthodox initiatives."

The CIA supported SID, the Italian defence intelligence service, financially, but Gen Maletti's US counterparts were rarely willing to share information. There may have been good reason for the American caginess. In a posthumous memoir published last year, the wartime resistance hero Count Edgardo Sogno described how he visited the CIA station chief in Rome in July 1974 to inform him of his plans for an anti-communist coup.

"I told him that I was informing him as an ally in the struggle for the freedom of the west and asked him what the attitude of the American government would be," Mr Sogno wrote. "He answered what I already knew: the United States would have supported any initiative tending to keep the communists out of government."

Despite contacts with his CIA counterparts, no word of the Sogno plot was uttered. "I, for one, didn't know about the Sogno thing. I knew Mr Sogno was being investigated by a Turin magistrate but I didn't know he had such important contacts with US agencies in the United States and Italy," Gen Maletti said. "Clearly, Sogno had great confidence in the complicity of the American service."

The lucid 79-year-old general, whose English is almost perfect, has spent his retirement in South Africa painting and writing his memoirs, which are due to be published soon. He admits to feeling nostalgic for his homeland.

But the judges who convicted him in absentia last year were far from convinced of his gentlemanly qualities. In their written verdict they said he had obstructed an investigation into a 1973 attack on the interior minister by withholding crucial information from the magistrates.

Four members of the public were killed and 45 injured when an anarchist, Gianfranco Bertoli, hurled a grenade into a crowd outside police headquarters in Milan. Bertoli, according to the judges, was really a man of right-wing sympathies and a long-standing SID informant, codenamed Negro. Gen Maletti's men were warned in advance of the attack on the minister, Mariano Rumor, but took no action to prevent it and failed to pass on their information on Bertoli even after the killings.

Gen Maletti's role at the heart of the complex intrigues makes him an illuminating witness. Italy must clarify the mysteries of that time if it is to recover its national dignity and sovereignty, he said.

"Among the larger western European countries, Italy has been dealt with as a sort of protectorate. I am ashamed to think that we are still subject to special supervision."