* Twenty three hostages killed - provisional toll
* Many foreigners still unaccounted for
* Military clearing plant of mines after "final assault"
* Overall toll still unclear, although dozens feared dead
By Lamine Chikhi and Abdelaziz Boumzar
ALGIERS/IN AMENAS, Algeria, Jan 19 (Reuters) - The Algerianarmy carried out a dramatic final assault to end a siege byIslamist militants at a desert gas plant on Saturday in which 23hostages were killed, many of them believed to be foreigners,the interior ministry said.
Thirty-two al Qaeda-linked militants were killed in thearmy operation to recapture the complex, according to aprovisional toll from the ministry. A statement said 107 foreignhostages and 685 Algerian hostages had survived.
Militants seized the remote compound in the Sahara desert before dawn on Wednesday, taking a large number of hostages,including foreigner workers, and booby-trapped the compound withexplosives.
The crisis marked a serious escalation of unrest innorthwestern Africa, where French forces have been in Mali sincelast week fighting an Islamist takeover of Timbuktu and othertowns.
The gas plant near the town of In Amenas was home toexpatriate workers from Britain's BP, Norway's Statoil, Japanese engineering firm JGC Corp and others. OneAmerican and one British citizen have been confirmed dead.
British Prime Minister David Cameron said on Saturday hefeared for the lives of five British citizens still unaccountedfor. Statoil said five of its workers, all Norwegian nationals,were still missing. Japanese and American workers are alsounaccounted for.
"We feel a deep and growing unease ... we fear that over thenext few days we will receive bad news," Statoil Chief ExecutiveHelge Lund said on Saturday. "People we have spoken to describeunbelievable, horrible experiences."
The Islamists' attack has tested Algeria's relations withthe outside world, exposed the vulnerability of multinationaloil operations in the Sahara and pushed Islamist radicalism innorthern Africa to centre stage.
British Foreign Secretary William Hague confirmed thatAlgerian military operations at the plant had been concluded.
"We understand that the site is not yet fully safe becauseof hazards such as booby traps and so they are still working onthat," Hague said.
Some Western governments expressed frustration at not beinginformed of the Algerian authorities' plans to storm thecomplex. Algeria's response to the raid will have beenconditioned by the legacy of a civil war against insurgents inthe 1990s which claimed 200,000 lives.
HOSTAGES FREED
As the army closed in, 16 foreign hostages were freed, asource close to the crisis said. They included two Americans andone Portuguese.
BP's chief executive Bob Dudley said on Saturday four of its18 workers at the site were missing. The remaining 14 were safe.
The captors said their attack on the Algerian gas plant wasa response to the French offensive in Mali. However, officialssay the elaborate raid would have been planned well beforeFrance launched its strikes.
Scores of Westerners and hundreds of Algerian workers wereinside the heavily fortified gas compound when it was seized onWednesday.
Hundreds escaped on Thursday when the army launched a rescueoperation, but many hostages were killed.
Before the interior ministry released its provisional deathtoll, an Algerian security source said eight Algerians and atleast seven foreigners were among the victims, including twoJapanese, two Britons and a French national. One British citizenwas killed when the gunmen seized the hostages on Wednesday.
The U.S. State Department said on Friday one American,Frederick Buttaccio, had died but gave no further details.
U.S. Defense Secretary Leon Panetta said nobody was going toattack the United States and get away with it.
"We have made a commitment that we're going to go after alQaeda wherever they are and wherever they try to hide," he saidduring a visit to London. "We have done that obviously inAfghanistan, Pakistan, we've done it in Somalia, in Yemen and wewill do it in North Africa as well."
BURNED BODIES
Earlier on Saturday, Algerian special forces found 15unidentified burned bodies at the plant, a source told Reuters.
The field commander of the group that attacked the plant isa fighter from Niger called Abdul Rahman al-Nigeri, according toMauritanian news agencies. His boss, Mokhtar Belmokhtar, aveteran of fighting in Afghanistan and Algeria's civil war ofthe 1990s, appears not to have joined the raid.
Britain, Japan and other countries have expressed irritationthat the army assault was ordered without consultation andofficials grumbled at the lack of information.
But French President Francois Hollande said the Algerianmilitary's response seemed to have been the best option giventhat negotiation was not possible.
"When you have people taken hostage in such large number byterrorists with such cold determination and ready to kill thosehostages - as they did - Algeria has an approach which to me, asI see it, is the most appropriate because there could be nonegotiation," Hollande said.
The apparent ease with which the fighters swooped in fromthe dunes to take control of an important energy facility, whichproduces some 10 percent of the natural gas on which Algeriadepends for its export income, has raised questions over thevalue of outwardly tough Algerian security measures.
Algerian officials said the attackers may have had insidehelp from among the hundreds of Algerians employed at the site.
Security in the half-dozen countries around the Saharadesert has long been a preoccupation of the West. Smugglers andmilitants have earned millions in ransom from kidnappings.
The most powerful Islamist groups operating in the Saharawere severely weakened by Algeria's secularist military in thecivil war in the 1990s. But in the past two years the regionalwing of al Qaeda gained fighters and arms as a result of thecivil war in Libya, when arsenals were looted from MuammarGaddafi's army.
France says the hostage incident proves its decision tofight Islamists in neighbouring Mali was necessary. AlQaeda-linked fighters, many with roots in Algeria and Libya,took control of northern Mali last year.
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