IN AMENAS, Algeria, Jan 18, 2013 (AFP) - Britain said on Friday that hostages were still being held at a remote Algeria gas field after a deadly rescue bid, as criticism mounted of Algiers' decision to resort to force against the Islamist captors.

An Algerian security source said that 18 of the hostage-takers had been killed in Thursday's air ground assault on a housing compound, but the remainder of the more than 30 militants remained holed up in the field's main production facility.

British Prime Minister David Cameron said the Algerian army was still pursuing "terrorists" and searching for hostages at the gas plant.

He said the first stage of the military operation was complete, "but 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."

Algerian Communications Minister Mohamed Said said the assault freed a "large number" of hostages, but news reports from Algiers said nearly 600 of those rescued were Algerian workers.

Of the 41 foreigners the militants had said they were holding, just a handful were released, the reports said.

The Islamist militants had seized hundreds of hostages at the field deep in the Sahara on Wednesday, purportedly to avenge a French-led offensive in neighbouring Mali.

BP said that a "small number" of its staff at In Amenas were unaccounted for on Friday, adding it had evacuated hundreds of workers from it and adjacent fields amid the "serious" hostage crisis.

"There is a small number of BP employees at In Amenas whose current location and situation remain uncertain," the British energy giant said.

Cameron said "significantly" fewer than 30 British citizens remained at risk.

Northern Ireland escape

Japanese plant builder JGC said it had confirmed the safety of three of its Japanese staff and one Filipino, but the whereabouts of 74 other staff, 14 of them Japanese, remained unknown.

Norway's Statoil, which operates the field along with BP and Algerian energy firm Sonatrach, said eight Norwegian staff remained unaccounted for, while a ninth was safe but had been wounded.

France said two of its nationals had returned safe but it had no word on two others reported to have been taken hostage.

One man from Northern Ireland escaped. According to his brother, Stephen McFaul fled when the convoy in which he was travelling came under fire from the army. He had earlier "had explosives tied around his neck."

The kidnappers said 34 captives had died in the assault, but an Algerian security source described the toll as "fantasy."

Japan's foreign ministry summoned the Algerian ambassador to demand an explanation why it had received no prior notice of the commando raid as Prime Minister Shinzo Abe cut short a visit to Indonesia to deal with the crisis.

Tokyo said the army assault was "regrettable" and that it was receiving no clear information from on the ground.

A senior US official said Washington "strongly encouraged" the authorities to make the hostages' safety their top priority.

The British premier confirmed that he too was not informed in advance of the assault.

The chief hostage taker, Abu al-Baraa, had told Al-Jazeera television: "We demand the Algerian army pull out from the area to allow negotiations."

But Algeria insisted it would not negotiate with "terrorists".

The International Energy Agency said the hostage-taking "cast a dark cloud over the outlook for the country's energy sector" as the jihadist splinter group which claimed the operation promised on Friday to stage more attacks.

"Taking into account the suffering of the Algerian people, we promise the regime in place that there will be more operations," a spokesman for the "Signatories in Blood" group told Mauritanian news agency ANI.

The hostage drama dragged Algiers and Western powers into the Mali conflict, taking the spotlight off French and government troops battling the Islamists in control of the country's vast desert north.

The Malian army has retaken the central of Konna, which had fallen to Islamists advancing from the north and sparked French military intervention, the military and a regional security source said on Friday.

On Thursday, more French troops poured into Mali, boosting their number to 1,400, Paris said. At full strength the force will reach 2,500 soldiers.

French Foreign Minister Laurent Fabius said he would attend an emergency summit of the west African bloc ECOWAS on Saturday to help accelerate the deployment of an African military force in Mali.