Algerian special forces have freed 650 hostages from Islamist militants who seized a gas complex deep in the desert, Algerian state media said Friday.
Of those taken hostage Wednesday, 573 were Algerians, according to the state-run Algerian Press Service news agency. It said "over half" of the 132 foreign workers held in the hostage crisis have been freed, according to a provisional count.
CNN has not independently confirmed the APS report.
Details of the total number of hostages seized at the In Amenas installation and their nationalities are still not clear.
The special forces are still trying to reach a "peaceful ending," APS cited a security force as saying, before "neutralizing" the terrorist group.
Some foreign workers have sought refuge in various parts of the Saharan site, the source told the news agency.
The gas field, about 60 kilometers (37 miles) west of the Libyan border and 1,300 kilometers (about 800 miles) from the Algerian capital, Algiers, is run by Algerian state oil company Sonatrach in partnership with Britain's BP and Norway's Statoil.
State-run Algerian Radio earlier cited an official source as saying that a major military raid launched Thursday was over but that there was "ongoing activity at various locations" near the plant.
British Prime Minister David Cameron said Friday morning that the Algerians were still pursuing terrorists and possibly hostages at the large and complex site.
The number of Britons unaccounted for is "significantly" fewer than 30, he told the House of Commons, but he declined to give an exact number because of the fluidity of the situation.
Britain was not informed in advance of Algeria's military operation Thursday, Cameron said. But he stressed that it was the militants -- whose leader was linked to an al Qaeda offshoot -- who were to blame for the attack.
Cameron said nationals from at least seven other countries were involved, as well as many Algerians.
U.S. Defense Secretary Leon Panetta, speaking in London, said the United States was working round the clock to ensure the safe return of its citizens.
"Regardless of the motivation of the hostage takers, there is no justification for the kidnapping and murder of innocent people," he said. "Terrorists should be on notice that they will find no refuge, not in Algeria, not in North Africa, not anywhere. Those who attack our country or our people will have no refuge."
U.S. authorities have not specified how many Americans are caught up in the attack. Officials from Norway, France, Malaysia and Japan have said their nationals are also among those involved.
And after a day of chaotic reports Thursday, many relatives of workers at the besieged plant are braced for bad news.
A U.S. C-130 military aircraft is evacuating between 10 and 20 people caught up in the hostage-taking, a U.S. defense official told CNN on Friday.
They will be flown to U.S. facilities in Europe, the official said, and the condition of those who are injured will be assessed on the flight. "We just don't know what kind of injuries they have," he said.
BP said Friday that a "small number of BP employees" are still unaccounted for, while Statoil said the fate of eight of its employees at In Amenas was still uncertain. Nine other Statoil workers who were at the plant are safe, it said.
Both firms are pulling personnel from Algeria. BP said it had flown 11 of its own employees and several hundred staff from other companies out of the North African country Thursday and expected another flight Friday.
Britain has deployed a diplomatic "rapid reaction" plane to a location about 280 miles from the besieged plant, a Foreign Office official said.
On board are trauma experts and consular affairs officers who can issue emergency passports. "It's the kind of thing we have done before in similar situations," the official said. "This is us getting as close and as ready as we can."
A Briton was one of two people confirmed killed Wednesday.
Algeria faces tough questions from the governments of kidnapped nationals over its handling of the crisis amid fears that hostage safety is not being put first.
Japanese Vice Minister Shunichi Suzuki summoned the Algerian ambassador Friday to express Tokyo's concern, the Japanese Foreign Ministry said. And Japanese Prime Minister Shinzo Abe is cutting short a foreign trip to deal with the crisis, his office said.
"There is so much conflicting information on safety of the hostages," Chief Cabinet Secretary Yoshihide Suga told reporters in Tokyo. "Safety of 14 Japanese citizens still remains unknown."
He said Japanese officials had urged the Algerian government to avoid exposing the hostages to danger. "We are terribly disappointed about the Algerians' military operation," he said.
Before the Algerians launched the military operation, U.S. officials urged them to be cautious and make the hostages' safety their first priority, an Obama administration official said.