With Western leaders clamoring for details of the assault they said Algeria had launched on Thursday without consulting them, a local source said the gas base was still surrounded by Algerian special forces and some hostages remained inside.
Thirty hostages, including several Westerners, were killed during the storming, the source said, along with at least 11 of their captors, who said they had taken the site as retaliation for French intervention against Islamists in neighboring Mali.
The crisis represents a serious escalation of unrest in North Africa, where French forces have been in Mali since last week to fight an Islamist takeover of the north, and strikes a heavy blow to Algeria's vital oil industry, just recovering from years of civil war.
Fourteen Japanese were among those still unaccounted for by the early hours of Friday, their Japanese employer said, while Norwegian energy company Statoil, which runs the Tigantourine gas field with Britain's BP and Algeria's national oil company, said eight Norwegian employees were still missing.
A French hostage employed by a French catering company said Algerian military forces were combing the sprawling In Amenas site for hostages when he was escorted away by the military.
"They are still counting them up," Alexandre Berceaux told Europe 1 radio.
The crisis posed a serious dilemma for former colonial power Paris and its allies as French troops attacked the hostage-takers' al-Qaida allies in Mali, another former colony.
The kidnappers warned Algerians to stay away from foreign companies' installations in the OPEC-member oil and gas producing state, threatening more attacks, Mauritania's news agency ANI said, citing a spokesman for the group.
Algerian workers form the backbone of an oil and gas industry that has attracted international firms in recent years partly because of military-style security. The kidnapping, storming and further threat cast a deep shadow over its future.
An Irish engineer who survived said he saw four jeeps full of hostages blown up by Algerian troops whose commanders said they moved in about 30 hours after the siege began because the gunmen had demanded to be allowed to take their captives abroad.
Two Japanese, two Britons and a French national were among at least seven foreigners killed, the source told Reuters. Eight dead hostages were Algerian. The nationalities of the rest, and the perhaps dozens more who escaped, were unclear. Some 600 local Algerian workers, less well guarded, survived.
Norwegian Foreign Minister Espen Barth Eide said his country still did not know the fate of eight of 13 Norwegian hostages taken. "As we understand it, the operation is still ongoing," he told Britain's BBC broadcaster.
Japanese Prime Minister Shinzo Abe has cancelled part of his trip in Southeast Asia, his first overseas trip since taking office, and will fly home due to the hostage crisis, Japan's senior government spokesman said on Friday.
"The action of Algerian forces was regrettable," said Japan's Chief Cabinet Secretary Yoshihide Suga, adding Tokyo had not been informed of the operation in advance.
Their governments say Americans, Romanians and an Austrian have also been captured by the militants, who have demanded France end its week-old offensive in Mali.
A US plane landed near the plant to evacuate hostages, the local source said on Friday.
Underlining the view of African and Western leaders that they face a multinational Islamist insurgency across the Sahara - a conflict that prompted France to send hundreds of troops to Mali last week - the official source said only two of the 11 dead militants were Algerian, including the squad's leader.
The bodies of three Egyptians, two Tunisians, two Libyans, a Malian and a Frenchman - all assumed to have been hostage-takers - were found, the security source said.
The group had claimed to have dozens of guerrillas on site, and it was unclear whether any militants had managed to escape.
The overall commander, Algerian officials said, was Mokhtar Belmokhtar, a veteran of Afghanistan in the 1980s and Algeria's bloody civil war of the 1990s. He appears not to have been present and has now risen in stature among a host of Saharan Islamists, flush with arms and fighters from chaotic Libya, whom Western powers fear could spread violence far beyond the desert.
Algerian security specialist Anis Rahmani, author of several books on terrorism and editor of Ennahar daily, told Reuters about 70 militants were involved from two groups, Belmokhtar's group, who traveled from Libya, and the lesser known "Movement of the Islamic Youth in the South".
"They were carrying heavy weapons including rifles used by the Libyan army during (Muammar) Gadhafi's rule. They also had rocket-propelled grenades and machine guns."
ALGIERS (Reuters) -- At least 22 foreign hostages were unaccounted for on Friday and their al-Qaida-linked captors threatened to attack other energy installations after Algerian forces stormed a desert gas complex to free hundreds of captives, resulting in dozens of deaths.