ALGIERS (Reuters) - Algeria's government spokesman confirmed some hostages were killed in a continuing military operation at a desert gas plant on Thursday but said troops had been forced to act to free them due to the "diehard" attitude of their captors.

In the first official comments by the government on the day's events, Communication Minister Mohamed Said was quoted as telling state news agency APS that many militants had been killed and that efforts to free foreign hostages were going on.

He acknowledged there had been "several deaths and injuries" among the hostages, but insisted Algeria, which fought a bloody war against Islamists through the 1990s, would not negotiate.

"We say that in the face of terrorism, yesterday as today as tomorrow, there will be no negotiation, no blackmail, no respite in the struggle against terrorism," APS quoted Said as saying.

Adding that Algerian forces had done all they could to ensure the hostages' survival and bring the siege to a successful conclusion, he blamed "the diehard attitude of the terrorists" for forcing the military to launch its operation.

Western leaders whose citizens are among the hostages, including British Prime Minister David Cameron, said they were told of the assault only after it started. He told Britons to prepare for "bad news" and an aide said Cameron would have preferred to have been consulted before the raid began.

Said said the militants' goals had been to destabilize Algeria and draw it in to the civil war in Mali.

The guerrillas had demanded that France stop its offensive against Mali's Islamist rebels and that Algerian withdraw its cooperation with the French operation.

(Reporting by Lamine Chikhi; Editing by Alastair Macdonald)