A diplomatic row broke out between London and Rome on Friday over Britain's failure to inform the Italian government before launching a botched hostage rescue mission in Nigeria.
The raid resulted in the deaths of a Briton and an Italian held hostage by what Nigerian authorities said was a militant Islamist group.
Chris McManus and Italian Franco Lamolinara had been kidnapped last May while working for a construction company in northwest Nigeria.
British Prime Minister David Cameron said they were killed by their captors in a rescue mission involving Nigerian and British special forces and his government confirmed the Italians had not been informed until after the operation began.
President Giorgio Napolitano led a chorus of Italian condemnation on Friday, saying: The behaviour of the British government in not informing Italy is inexplicable.
A political and diplomatic clarification is necessary.
Italian Foreign Minister Giulio Terzi later discussed the issue with his British counterpart William Hague at an informal foreign ministers meeting in Copenhagen.
He told Hague of the enormous pain caused to an Italian family due to what happened, ANSA news agency reported.
According to a joint statement issued after the meeting, Hague explained there had only been a limited opportunity to try to free the hostages from a compound in the town of Sokoto, because their lives were in imminent danger.
Under these circumstances it was only possible to inform Italy once the operation was already getting underway, said the statement released by the British foreign office.
Mr Terzi expressed deep sorrow and disappointment over the tragic outcome of the operation and both ministers agreed on the urgency of sharing full information to facilitate the reconstruction and understanding of these events.
Earlier British Defence Secretary Philip Hammond told the BBC that intelligence showed the two men were about to be moved and possibly executed.
Asked whether the Italians had approved the operation, Hammond said: They were informed of it. I don't think they specifically approved it, they were informed of what was happening.
However, Italian politicians expressed unhappiness about how the matter had been handled.
Italy wasn't informed or asked its opinion about a blitz that put at mortal risk an Italian citizen, Fabrizio Cicchitto, a senior official in former Prime Minister Silvio Berlusconi's People of Liberty party, said in a television interview.
Between allies, this sort of mission is usually talked about beforehand. The British government bypassed and completely ignored us, he said.
While Italian media criticised Britain for acting unilaterally, commentators also said the event underscored Italy's diminishing international clout.
They linked the incident to an ongoing struggle by Italy to free two marines on anti-piracy duty who are being held in India for shooting dead two fishermen in the Indian Ocean.
The United Kingdom still acts, maybe unconsciously, with the nostalgia of imperial glory, said Antonio Puri Purini in Corriere della Sera, the country's biggest daily.
The British ambassador in Rome visited the Italian Foreign Ministry on his own accord on Thursday night, a British Foreign Office spokeswoman said without giving further details.
A Downing Street spokesman said Britain had been in close contact with the Italian government since the kidnapping last May. Rome was contacted as the operation got underway, he said.
The fact of the matter is things were moving quite quickly on the ground and we had to respond to that and our top priority was to maximize the chances of getting the hostages out.
Asked if Italy's premier had given prior approval to a rescue operation, he said: When the prime minister (Cameron) phoned (Italian Prime Minister) Mario Monti, the operation had happened. We knew that the hostages were dead.
Monti also spoke to Nigerian President Goodluck Jonathan, whose special forces made up most of the attack force, on Thursday to demand a complete reconstruction of the operation.
A senior official at Nigeria's State Security Service said the hostage takers were a faction of militant Islamist sect Boko Haram that has links with al Qaeda's north African wing. A purported spokesman for the group phoned journalists on Friday to deny any link.
Boko Haram is waging an insurgency against Nigeria's southern dominated government and has been blamed for shootings and bombings that have killed hundreds in the last two years.
The two diplomatic incidents in Nigeria and India are an unexpected challenge for Monti, who has focused primarily on economic reforms.
He took power at the head of an unelected government of technocrats in November, replacing the scandal-plagued Berlusconi as Italy teetered on the brink of ruinous default.
Despite being a NATO member and active in international peacekeeping - with troops in Afghanistan, Kosovo, Lebanon and elsewhere - Italy's international influence seems to have flagged in recent years.
Berlusconi's flamboyant personality, sexual and corruption scandals and diplomatic gaffes damaged Italy's reputation abroad, especially after his foot-dragging when Britain and France pushed for the NATO bombing campaign that helped oust Libya's Muammar Gaddafi.
(Additional Reporting By Catherine Hornby in Rome, Avril Ormsby, Michael Holden and Estelle Shirbon in London, Tim Cocks in Lagos and Camillus Eboh in Abuja; editing by Barry Moody, Philip Pullella and Jon Boyle)