ALGIERS, Algeria -- Algerian de-mining teams were scouring a gas refinery on Sunday that was the scene of a bloody four-day standoff, searching for explosive traps left by the Islamist militants who took dozens of foreigners hostage. The siege left at least 23 captives dead, and the American government warned that there were credible threats of more kidnapping attempts on Westerners.
Algerian special forces stormed the natural gas complex in the Sahara desert on Saturday to end the standoff, and the government said all 32 militants were killed.
The chief government spokesman, Mohamed Said, said Sunday the final toll of hostages killed would be known within hours, but that he "strongly feared it would rise."
He said the militants came from six countries and were armed to cause maximum destruction.
"They had decided to succeed in the operation as planned, to blow up the gas complex and kill all the hostages," Said said.
With few details emerging from the remote site in eastern Algeria, it was unclear whether anyone was rescued in the final operation, but the number of hostages killed on Saturday - seven - was how many the militants had said that morning they still had. The government described the toll as provisional and some foreigners remained unaccounted for.
British Prime Minister David Cameron said Sunday three Britons were killed and another three are believed dead, as is a British resident.
"Now of course people will ask questions about the Algerian response to these events, but I would just say that the responsibility for these deaths lies squarely with the terrorists who launched a vicious and cowardly attack," Cameron said.
The siege at Ain Amenas transfixed the world after radical Islamists linked to al-Qaida stormed the complex on Wednesday, which contained hundreds of plant workers from all over the world, then held them hostage surrounded by the Algerian military and its attack helicopters for four tense days that were punctuated with gun battles and dramatic tales of escape.
Algeria's response to the crisis was typical of its history in confronting terrorists, favoring military action over negotiation, which caused an international outcry from countries worried about their citizens. Algerian military forces twice assaulted the two areas where the hostages were being held with minimal apparent mediation - first on Thursday, then on Saturday.
"To avoid a bloody turn of events in response to the extreme danger of the situation, the army's special forces launched an intervention with efficiency and professionalism to neutralize the terrorist groups that were first trying to flee with the hostages and then blow up the gas facilities," Algeria's Interior Ministry said in a statement about the standoff.
De-mining teams began going through the complex late Saturday and Sunday, searching for explosive traps left behind by the militants, the state news service said, citing security officials that it did not name. Sonatrach, the Algerian state oil company running the Ain Amenas site along with BP and Norway's Statoil, said the entire refinery had been mined.
The State Department issued a travel warning Saturday night for Americans in or traveling to Algeria, citing credible threats of the kidnapping of Western nationals. The department also authorized the departure from Algeria of staff members' families if they choose to leave.
Immediately after the assault, French President Francois Hollande gave his backing to Algeria's tough tactics, saying they were "the most adapted response to the crisis."
"There could be no negotiations" with terrorists, the French media quoted him as saying in the central French city of Tulle.
Hollande said the hostages were "shamefully murdered" by their captors, and he linked the event to France's military operation against al-Qaida-backed rebels in neighboring Mali. "If there was any need to justify our action against terrorism, we would have here, again, an additional argument," he said.
In the final assault, the remaining band of militants killed seven hostages before 11 of them were in turn cut down by the special forces, Algeria's state news agency said. The military launched its Saturday assault to prevent a fire started by the extremists from engulfing the complex and blowing it up, the report added.
A total of 685 Algerian and 107 foreigner workers were freed over the course of the four-day standoff, the Interior Ministry statement said, adding that the group of militants that attacked the remote Saharan natural gas complex consisted of 32 men of various nationalities, including three Algerians and explosives experts.
The military also said it confiscated heavy machine guns, rocket launchers, missiles and grenades attached to suicide belts.
Algeria has fought its own Islamist rebellion since the 1990s, elements of which later declared allegiance to al-Qaida and then set up new groups in the poorly patrolled wastes of the Sahara along the borders of Niger, Mali, Algeria and Libya, where they flourished.
The standoff has put the spotlight on al-Qaida-linked groups that roam these remote areas, threatening vital infrastructure and energy interests. The militants initially said their operation was intended to stop a French attack on Islamist militants in neighboring Mali - though they later said it was two months in the planning, long before the French intervention.
The militants, who came from a Mali-based al-Qaida splinter group run by an Algerian, attacked the plant Wednesday morning. Armed with heavy machine guns and rocket launchers in four-wheel drive vehicles, they fell on a pair of buses taking foreign workers to the airport. The buses' military escort drove off the attackers in a blaze of gunfire that sent bullets zinging over the heads of crouching workers. A Briton and an Algerian - probably a security guard - were killed.
The militants then turned to the vast gas complex, divided between the workers' living quarters and the refinery itself, and seized hostages, the Algerian government said. The gas flowing to the site was cut off.
The accounts of hostages who escaped the standoff showed they faced dangers from both the kidnappers and the military. The militants focused on the foreign workers from the outset, largely leaving alone the hundreds of Algerian workers who were briefly held hostage before being released or escaping.