BAMAKO, Mali — The Algerian army carried out a final assault on the gas field taken over by Islamist militants, killing most of the remaining kidnappers and raising the total of hostages killed to at least 23, Algerian officials said.

Although the government declared an end to the four-day siege, authorities believed a handful of jihadists were most likely hiding somewhere in the sprawling complex and said that troops were searching for them.

The details of what transpired in the Sahara and the final battle for the plant remained murky Saturday night — as did information of which hostages died and how — with even the White House suggesting that it was unclear what had happened. A brief statement released early Saturday night said the administration would “remain in close touch with the government of Algeria to gain a fuller understanding of what took place so that we can work together to prevent tragedies like this in the future.”

The British defense minister, Philip Hammond, called the loss of life “appalling and unacceptable,” after reports that up to seven hostages were killed Saturday in the final hours of the standoff. The Algerian government also announced that 32 militants had been killed since Wednesday, although it cautioned that the casualty counts were provisional.

Defense Secretary Leon Panetta, who appeared with Hammond at a news conference in London, said he did not yet have reliable information about the fate of Americans at the facility, although a senior Algerian official said two had been found “safe and sound.”

Britain’s foreign secretary, William Hague, emerged from a meeting of the British government’s crisis committee late Saturday night with the news that five Britons and one British resident had died in the final rescue attempt or were unaccounted for. He declined to provide details, saying the government had not yet received a full picture of what happened and that police forces were still fanning out across Britain visiting each of the families involved and giving them “the support they need at this very difficult time.”

One of the Algerian officials defended the military assault on Saturday, saying they feared the militants were about to set off explosions at the In Amenas complex.

Whatever the goal, the message of the ambitious assault on the well-defended gas complex, in a country that has perhaps the world’s toughest record for dealing with terrorists, seemed clear, at least to Algerian officials Saturday: The Islamist mini-state in northern Mali, now under assault by French and Malian forces, has given a new boost to transnational terrorism. The brigade of some 32 Islamists that took the plant was multinational, Algerian officials and some escaped hostages said — with only three of their own nation in the group.

“We have indications that they came from northern Mali, at the origin,” one of the senior officials said. “They want to establish a terrorist state. ”

While none of the facts he presented could be immediately confirmed, a Mali-based Algerian jihadist with ties to al-Qaida, Mokhtar Belmoktar, has claimed credit through spokesmen for the raid.

U.S. officials had said “seven or eight” Americans had been at the In Amenas field when it was seized by the militants Wednesday.

One American, Frederick Buttaccio, 58, of Katy, Texas, was confirmed dead on Friday, and the French government said one of its citizens, identified as Yann Desjeux, had also died before Saturday’s raid. An Algerian state news agency said Algerians had also been killed as of Friday.

The militants who attacked the plant said it was in retaliation for French troops sweeping into Mali this month to stop an advance of Islamist rebels south toward the capital. However, the militants later said they had been planning an attack in Algeria for two months on the assumption that the West would intervene in Mali.

The Algerian state oil company, Sonatrach, said Saturday that the attackers had evidently mined the facility with the intention of blowing it up and that the company was working to disable the mines.

The brazenness of the assault — dozens of fighters attacking one of the country’s most important gas-producing facilities — is likely to call into question Algeria’s much vaunted security strategy.

Algeria may have to rethink its approach, analysts suggest, and engage in a more frontal strategy against the Islamists.