At least 48 hostages are now thought to have died in a four-day siege at In Amenas gas facility in Algeria, as reports say that 25 bodies found at the complex on Sunday were all those of captives.
It had initially been unclear whether the bodies found were those of hostage-takers or staff at the facility.
A search is continuing at the In Amenas gas plant, where as many as 20 hostages remain unaccounted for.
Five suspected Islamist attackers were reportedly arrested on Sunday.
The Algerian authorities had said on Saturday that all 32 hostage-takers had been killed. The suspected organizer of the attack, Mokhtar Belmokhtar, has said in a statement that 40 militants took part.
The siege was ended in a raid by troops on Saturday. Officials say a definitive death toll will be released later.
Officials said the army launched its assault after Islamist militants began killing foreign hostages.
UK Prime Minister David Cameron and US President Barack Obama have blamed “terrorists” for the hostages’ deaths.
And on Sunday French Defence Minister Jean-Yves Le Drian described the hostage-taking as an “act of war”.
“What strikes me the most is that we’re saying <<hostage-taking>> but when there are so many people concerned, I think this is an act of war,” he told French TV.
As Western leaders condemned the kidnappings, Algerian Energy Minister Youcef Yousfi said Algeria would boost security at its energy installations without outside help.
“It is out of the question to allow foreign security forces to handle the security of our oil facilities,” he said, quoted by Algeria’s APS news agency.
During a visit to the affected plant, Youcef Yousfi said it would resume production within two days.
The private TV channel Ennahar said security forces had discovered the bodies of 25 hostages as they searched the complex for booby-traps and mines.
The militants had threatened to blow up the site and kill their hostages, officials said.
Mokhtar Belmokhtar, who is not thought to have been among the actual attackers, said his group had carried out the attack. He was speaking in a video message carried by the Mauritanian website Sahara Media.
The website said the video had been recorded on January 17 while the siege was still going on but not posted on the website.
It shows Mokhtar Belmokhtar, who has convictions in absentia for murder, kidnapping and terrorism, saying he was prepared to negotiate with Western and Algerian leaders if operations against Islamists in Mali were stopped.
In other developments:
- Six Filipinos were killed and four are missing, the government in Manila confirmed
- Three Britons were confirmed dead, and a further three are missing, feared dead. UK officials were “working hard” to locate the missing, said Foreign Secretary William Hague
- A Colombian citizen resident in the UK, Carlos Estrada, is thought to be among the dead, the Colombian president has said
- Japanese officials said they had no confirmation of the fate of 10 nationals who remained unaccounted for, despite reports that nine had died
- Romania’s foreign ministry said one of its citizens had died in hospital after sustaining severe injuries during the siege. Another Romanian has already been reported killed and as many as three others have been freed
- Two Malaysians are unaccounted for, as are five Norwegians
State news agency APS said 685 Algerian workers and 107 out of 132 foreigners working at the plant had been freed, citing interior ministry figures.
The nationalities of some of the hostages killed are still not known.
The crisis began on Wednesday when militants attacked two buses carrying foreign workers to the remote site in south-eastern Algeria. A Briton and an Algerian reportedly died in the incident.
The militants then took Algerians and expatriates hostage at the complex, which was quickly surrounded by the Algerian army.
A statement from the kidnappers said the assault on the gas plant was launched in retaliation for French intervention against Islamist groups in neighboring Mali.
However, France only decided last week to intervene militarily in Mali. Analysts say the assault on the gas facility was well-planned and would have required advance research, as well as possibly inside help.