The UK and Italy were embroiled in a diplomatic row tonight over the failed hostage rescue bid in Nigeria.
Italian president Giorgio Napolitano branded Downing Street's failure to inform Rome "inexplicable".
British construction worker Chris McManus and his Italian co-worker Franco Lamolinara died yesterday as Nigerian troops and UK Special Boat Service (SBS) commandos tried to end their nine months in captivity.
The bid to rescue the men was apparently brought forward because the kidnappers - believed to be members of a jihadi group associated with al Qaida - became aware that the net was closing around them.
There were reports of a fierce firefight after the house in the north-western town of Sokoto was surrounded.
Number 10 said that contacts had taken place between the governments as the operation got under way, and that David Cameron later spoke to Italian prime minister Mario Monti by phone after it was learned that the hostages were dead.
Mr Cameron's spokesman said he was not aware of any request from Rome to halt the operation or of any complaint from Mr Monti during the phone call.
Mr Cameron did not offer any apology for the way in which the mission unfolded.
It had been clear for some time that one option was an attempt to rescue the two men, and Downing Street was not aware of Italy raising any objection to a possible mission, according to the spokesman.
Mr Monti disclosed the lack of warning in a statement in which he said UK and Nigerian authorities had determined the operation was the "last window of opportunity to save the hostages' lives".
Mr Napolitano told reporters: "The behaviour of the British Government in not informing Italy is inexplicable. A political and diplomatic clarification is necessary."
Italian diplomat Antonio Puri Purini said the events had been an "unacceptable slap in the face" for his countrymen.
Writing in the leading Italian newspaper Corriere della Sera, he claimed Britain's nostalgia for its imperialist days had led it to act alone.
But Mr Cameron's spokesman told reporters at a regular Westminster briefing: "We had been in contact with the Italians on a regular basis over the past nine months.
"We have had many, many meetings in the UK on this issue. There have been around 20 meetings of Cobra to discuss this particular case and throughout that period we have been in contact with the Italians.
"An option was always a rescue operation. We have been keeping them informed throughout."
He added: "Things moved quite quickly in recent days and we had to respond to that. The Prime Minister was asked for authorisation and gave that authorisation, but this was a Nigerian-led operation.
"In any situation such as this, we need to take the advice of those people on the ground closest to the situation. Their very strong advice was that it was important to act and to act quickly and that that was the best chance of getting these people out.
"Early indications are that both men were murdered by their captors before they could be rescued."
Defence Secretary Philip Hammond directly contradicted the Italian president's comments.
He told the BBC: "Well it isn't inexplicable. It's completely explicable what happened. It's very unfortunate, but it's completely explicable."
Asked why the Italian authorities were not consulted, he said: "The Italian government was kept informed throughout the operation as the intelligence emerged and then as the decision was taken to act, the Italian authorities were informed."
However, Mr Hammond said that although they were told about the operation, they did not authorise it.
"They were informed on it," he said. "I don't think they specifically approved it, they were informed of what was happening."
The Defence Secretary went on: "There was intelligence that they were about to be moved, possibly executed, and therefore the decision was to go in, aware of course that there were huge risks.
"Hostage rescue exercises always have huge risks attached ... but the decision was made that the best chance of saving their lives was to act."
Mr Cameron said last night that Mr McManus and Mr Lamolinara had been in "imminent and growing danger" and an opportunity had arisen to attempt to rescue them.
"The terrorists holding the two hostages made very clear threats to take their lives, including in a video that was posted on the internet," he said.