Algerian forces still looking for hostages: Cameron
"The operation is still on," British Prime Minister David Cameron said, 36 hours after Algerian special forces stormed the complex in which Algerian authorities said four foreign workers and 18 militants were killed.
Making a statement in parliament on the deadly rescue bid, Cameron said "hostages were still being held in the complex".
BBC said the militants had claimed to be holding 41 foreigners and at least four were freed but the fate of many others was still unknown.
British Petroleum which runs the complex in collaboration with the Algerians said it had evacuated hundreds of workers from international oil companies and that many more would follow.
Cameron told parliament that the Algerian Army was still pursuing the terrorists and searching for hostages at the site. He said only the first part of the operation was complete.
"This is a large and complex site and they are still pursuing terrorists and possibly some of the hostages in other areas of the site," he said.
The militants had claimed strafing by Algerian helicopters killed 35 hostages and 15 kidnappers, a figure disputed by the Algerian authorities.
The state-run APS news agency cited local officials as saying two Britons and two Filipinos were killed.
Two others, a Briton and an Algerian, died on Wednesday when the militants ambushed a bus that was taking foreign workers at the facility to the local airport, BBC said.
The British Prime Minister said 30 Britons were still unaccounted for but the number is now considerably reduced. As he announced that his government had added extra protection for diplomatic and energy facilities in Algeria.
Giving details of the attack, Cameron said the Islamist gunmen first attacked two buses en route to the airfield at the remote desert complex on Wednesday, killing two men.
Later, he said, they attacked a residential compound at the plant before turning to the gas facility itself.
The plant is located just few kilometres from the Libyan border.
Among the foreign workers who were unaccounted for were Americans, Britons, French, Norwegians, Malaysians, Japanese and Filipinos, and there was anger in these countries over the Algerian raid that appeared to have gone wrong.
French Interior Minister Manuel Valls described the situation as "still murkey".
US Defence Secretary Leon Panetta, who is on a visit to London, said that Washington and London were working closely with the Algerian government to assess what is happening on the ground.
Speaking on Friday at the King's College London, Panetta said the US is working to round the clock to ensure a safe return of its citizens.
"We deeply regret the actions taken by the Algerian military," Yoshihide Suga, Japanese Chief Cabinet Secretary said even as the Japanese foreign ministry summoned the Algerian ambassador.
Japanese officials were quoted as saying by the Kyodo news agency that at least 14 Japanese nationals were still missing while at least three had managed to escape.
The UK, Japan and US said they had not been informed in advance about the military assault.
Algerian Communications Minister Mohand Said Oubelaid, however, said: "Those who think we will negotiate with terrorists are delusional."
Cameron said the Algerian prime minister had told him that commanders had "judged there to be an immediate threat to the lives of the hostages and had felt obliged to respond".