BAMAKO, Mali -- Algerian officials said Sunday that the death toll from the four-day hostage siege at a gas-producing complex in the Sahara was growing as security forces combed the site and discovered more corpses, some badly burned.
A senior Algerian official said "a good 20" more bodies were found Sunday morning, though it was unclear whether they were militants or hostages. The official said that at least seven Americans were "liberated," and that some militants were captured.
"There are corpses that haven't been identified," the official said.
Once they are, the preliminary count of 23 dead hostages seemed certain to rise, officials acknowledged.
"I'm very afraid that the numbers are going to go up," the Algerian communications minister, Mohamed Said Belaid, told France 24 Television. Over a dozen hostages were still missing on Sunday, including some Americans, officials said.
The confrontation at a remote gas field taken over by militants ended Saturday as the Algerian Army carried out a final assault. The details of the desert standoff and the final battle for the plant remained murky -- as did information about which hostages died and how.
Still, new details emerged on Sunday. The attackers were a multinational group from six countries, Mr. Belaid told the official APS news agency. He would not identify the countries by name, but other senior officials said that there were indications that the group originated in northern Mali and was once linked to Al Qaeda in the Islamic Maghreb, Al Qaeda's North African branch.
It was not clear how many attackers were involved, although Algerian officials said at least 32 were killed. For the first time on Sunday, Afghan officials said that some attackers were captured, contrary to earlier reports that they were all killed.
An Algerian jihadist, Mokhtar Belmokhtar, who is based in Mali and has ties to Al Qaeda, has claimed responsibility through spokesmen for masterminding the raid. Algeria also blames him for the attack.
The militants said the assault was carried out in retaliation for the French troops sent to Mali this month to stop an advance of Islamist rebels south toward the capital, although they later said they had been planning an attack in Algeria for some time.
The fighting began with heavy gunfire early Wednesday, and continued through a fierce, helicopter-led government assault on Thursday. Most of the hundreds of workers at the plant, who came from about 25 countries, appeared to escape sometime during the four days.
The total number of people who were held hostage remained unclear on Sunday. There was also some questions about the aggressive tactics used by the Algerian Army. Western leaders have criticized the Algerian government for failing to consult them before the military action.
Initial reports from Algerian state news media said that seven workers had been executed during the army's raid, but the senior government official and another high-level official, both of whom spoke on the condition of anonymity, later said the number killed and the causes of death were unknown.
What little information trickled out from survivors was harrowing. Some hostages who managed to escape told of workers being forced to wear explosives. They also said that there were several summary executions and that some workers had died in the military's initial rescue attempt.
Alan Wright, a British survivor, said in an interview with Sky News that he spent about two days hiding in an office complex with about 30 workers listening to the sounds of gunfire outside. The majority, he said, were Algerian citizens who he said could have left him and his colleagues. Instead, he said, they helped them escape by dressing them as local residents and cutting through several perimeter fences. They were rescued by Algerian soldiers.
"I can't say enough about the guys in our building, who had the option to surrender and be safe," he said. "You'll be in debt to them for the rest of your life."
He also praised the Algerian military: "If it weren't for them, I think it would have been a lot worse."
In public remarks on Sunday, Western leaders called for a decisive and far-reaching response to the attack, indicating a willingness to expand military operations in North Africa to counter deeply rooted Islamist militant groups.
"We have had successes in recent years in reducing the threat from some parts of the world, but the threat has grown, particularly in North Africa," Prime Minister David Cameron of Britain said in a televised address.
"This is a global threat, and it will require a global response," he said. "It will require a response that is about years, even decades, rather than months. It requires a response that is patient and painstaking, that is tough but also intelligent, but above all has an absolutely iron resolve, and that is what we will deliver over these coming years."
He added: "What we face is an extremist, Islamist, Al Qaeda-linked terrorist group. Just as we had to deal with that in Pakistan and in Afghanistan, so the world needs to come together to deal with this threat in North Africa."
The French defense minister, Jean-Yves Le Drian, captured that sentiment succinctly, telling France 5 television that the attack on the oil facility was "an act of war."
Adam Nossiter reported from Mali, and Michael Schwirtz from New York. Reporting was contributed by Steven Erlanger and Scott Sayare from Paris; Alan Cowell, Elisabeth Bumiller, John F. Burns and Stanley Reed from London; Manny Fernandez and Clifford Krauss from Houston; and Eric Schmitt and Michael R. Gordon from Washington.
This article originally appeared in The New York Times.