"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. (MORE)
