The Italian Government was today embroiled in a row over claims that the Italian Red Cross secretly treated suspected terrorists in exchange for the release of two kidnapped aid workers in Iraq.

Maurizio Scelli, the outgoing commissioner of the Croce Rossa, told a newspaper that the scheme to free Simona Pari and Simona Torretta had been agreed without informing US officials.

Such a pact has been the subject of speculation since the two women returned to Italy last September amid rumours - strenuously denied - that a ransom was paid.

Signor Scelli's claims that they were freed in exchange for covert humanitarian aid has shocked many Italians, leading all major news bulletins today, and threatening to further strain the ties between Rome and Washington.

Relations have already been shaken by the "friendly fire" killing by US troops of Nicola Calipari, an Italian intelligence officer, in the middle of another hostage release operation by Italy. They soured further with the CIA seizure of Hassan Mustafa Osama Nasr, a leading imam in Turin.

However, the story took a sudden twist at noon today when the Prime Minister's office released a statement from the Palazo Chigi saying that the Red Cross had acted independently and without the knowledge or approval of the Government.

"The Government of the (Italian) Republic and its offices have never conditioned or influenced (Red Cross) operations, which are carried out in full autonomy," it said.

Shortly afterwards, Signor Scelli appeared on RAI state television retracting his central claim that Gianni Letta, a close confidante of Silvio Berlusconi, had personally approved the secret deal, and sworn the Red Cross to secrecy with the words: "Nobody should know about it. Above all, the Americans should not know."

In the original interview, he told La Stampa, one of the largest Italian daily newspapers: "The mediators asked us to treat and save the lives of four presumed terrorists sought by the Americans, wounded in combat. We hid them and brought them to the doctors with the Red Cross, who operated on them.

"Keeping the Americans in the dark about our efforts to free the hostages was a non-negotiable condition to guarantee the safety of the hostages and ourselves."

He said that Italian medics had also treated four Iraqi children with leukaemia at a hospital in Baghdad.

Calipari was shot dead by US troops at a roadblock as he was escorting the freed hostage Giuliana Sgrena to Baghdad airport on March 4.

Rome and the Pentagon produced conflicting reports, with Italy insisting that American officers had been kept fully informed about the negotiations, while the US that its officers were largely in the dark.

The two war allies are also engaged in a row over the seizure of Nasr, a Muslim terrorism suspect, in 2003: the CIA maintains that the head of Italy's secret service authorised the abduction, but a judge in Turin has now issued arrest warrants for the 13 alleged members of the CIA team.

Members of the centre-left Opposition today capitalised on the low public support for the operations in Iraq, claiming that Italy has become a "disposable" ally for Washington. They called on the government to clarify the apparent contradictions between the accounts of the hostage release.

Richard Owen, correspondent for The Times in Rome, said: "This story has been all over the news since it broke this morning, and shows that the question of how Italy managed to secure the release of some of its hostages remains controversial.

"There has been speculation that ransoms were paid in some cases, but this practice has always been officially denied.

"This is not the first time that it has been suggested that Italy kept America in the dark, and although publicly the Italian Government says that their relations have been unimpaired there have clearly been tensions behind the scenes."

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