Dueling claims from the military and the militants muddied the world’s understanding of an event that angered Western leaders, raised world oil prices and complicated the international military operation in neighboring Mali.

At least six people, and perhaps many more, were killed – Britons, Filipinos and Algerians. Terrorized hostages from Ireland and Norway trickled out of the Ain Amenas plant, families urging them never to return.

Dozens more remained unaccounted for: Americans, Britons, French, Norwegians, Romanians, Malaysians, Japanese, Algerians and the fighters themselves.

The U.S. government sent an unmanned surveillance drone to the BP-operated site, near the border with Libya and 800 miles from the Algerian capital, but it could do little more than watch Thursday’s intervention. Algeria’s army-dominated government, hardened by decades of fighting Islamist militants, shrugged aside foreign offers of help and drove ahead alone.

With the hostage drama entering its second day Thursday, Algerian security forces moved in, first with helicopter fire and then special forces, according to diplomats, a website close to the militants, and an Algerian security official. The government said it was forced to intervene because the militants were being stubborn and wanted to flee with the hostages.

The militants – led by a Mali-based al-Qaida offshoot known as the Masked Brigade – suffered losses in Thursday’s military assault, but succeeded in garnering a global audience.

Even violence-scarred Algerians were stunned by the brazen hostage-taking Wednesday, the biggest in northern Africa in years and the first to include Americans as targets. Mass fighting in the 1990s had largely spared the lucrative oil and gas industry that gives Algeria its economic independence and regional weight.

The hostage-taking raised questions about security for sites run by multinationals that are dotted across Africa’s largest country. It also raised the prospect of similar attacks on other countries allied against the extremist warlords and drug traffickers who rule a vast patch of desert across several countries in northwest Africa. Even the heavy-handed Algerian response may not deter groups looking for martyrdom and attention.

Casualty figures in the Algerian standoff varied widely. The remote location is extremely hard to reach and was surrounded by Algerian security forces – who, like the militants, are inclined to advertise their successes and minimize their failures.

“An important number of hostages were freed and an important number of terrorists were eliminated, and we regret the few dead and wounded,” Algeria’s communications minister, Mohand Said Oubelaid, told national media, adding that the “terrorists are multinational,” coming from several different countries with the goal of “destabilizing Algeria, embroiling it in the Mali conflict and damaging its natural gas infrastructure.”

The official news agency said four hostages were killed in Thursday’s operation, two Britons and two Filipinos. Two others, a Briton and an Algerian, died Wednesday in an ambush on a bus ferrying foreign workers to an airport. Citing hospital officials, the APS news agency said six Algerians and seven foreigners were injured.

APS said some 600 local workers were safely freed in the raid – but many of those were reportedly released the day before by the militants themselves.

The militants, via a Mauritanian news website, claimed that 35 hostages and 15 militants died in the helicopter strafing. A spokesman for the Masked Brigade told the Nouakchott Information Agency in Mauritania that only seven hostages survived.

By nightfall, Algeria’s government said the raid was over. But the whereabouts of the rest of the plant workers was unclear.

President Barack Obama and British Prime Minister David Cameron spoke on the phone to share their confusion. White House Press Secretary Jay Carney said the Obama administration was “seeking clarity from the government of Algeria.”

An unarmed American surveillance drone soared overhead as the Algerian forces closed in, U.S. officials said. The U.S. offered military assistance Wednesday to help rescue the hostages but the Algerian government refused, a U.S. official said in Washington. He spoke on condition of anonymity because he was not authorized to speak publicly about the offer.

Militants earlier said they were holding seven Americans, but the administration confirmed only that Americans were among those taken. The U.S. government was in contact with American businesses across North Africa and the Middle East to help them guard against the possibility of copycat attacks.

BP, the Norwegian company Statoil and the Algerian state oil company Sonatrach, operate the gas field and a Japanese company, JGC Corp, provides services for the facility.

Japan’s Prime Minister Shinzo Abe protested the military raid as an act that “threatened the lives of the hostages,” according to a spokesman.

Jean-Christophe Gray, a spokesman for Cameron, said Britain was not informed in advance of the raid.

One Irish hostage managed to escape: electrician Stephen McFaul, who’d worked in North Africa’s oil and natural gas fields off and on for 15 years. His family said the militants let hostages call their families to press the kidnappers’ demands.

“He phoned me at 9 o’clock to say al-Qaida were holding him, kidnapped, and to contact the Irish government, for they wanted publicity. Nightmare, so it was. Never want to do it again. He’ll not be back! He’ll take a job here in Belfast like the rest of us,” said his mother, Marie.

Dylan, McFaul’s 13-year-old son, started crying as he talked to Ulster Television. “I feel over the moon, just really excited. I just can’t wait for him to get home,” he said.

At least one Filipino managed to escape and was slightly injured, the Philippine Foreign Affairs Department said. Spokesman Raul Hernandez said he had no information about any fatalities.

Algerian forces who had ringed the Ain Amenas complex had vowed not to negotiate with the militants, who reportedly were seeking safe passage. Security experts said the end of the two-day standoff was in keeping with the North African country’s tough approach to terrorism.

“Algerians clearly were not willing to compromise with the terrorists and not willing to accept the idea of coping with the situation for days and days,” said Riccardo Fabiani of Eurasia Group. “Algerians never had problems causing a blood bath to respond to terrorist attacks.”

Phone contacts with the militants were severed as government forces closed in, according to the Mauritanian agency, which often carries reports from al-Qaida-linked extremist groups in North Africa.

A 58-year-old Norwegian engineer who made it to the safety of a nearby Algerian military camp told his wife how militants attacked a bus Wednesday before being fended off by a military escort.

“Bullets were flying over their heads as they hid on the floor of the bus,” Vigdis Sletten told The Associated Press in a phone interview from her home in Bokn, on Norway’s west coast.

Her husband and the other bus passengers climbed out of a window and were transported to a nearby military camp, she said, declining to give his name for security reasons.

News of the bloody Algerian operation caused oil prices to rise $1.25 to close at $95.49 a barrel on the New York Mercantile Exchange, and prompted energy companies like BP PLC and Spain’s Compania Espanola de Petroleos SA to try to relocate energy workers at other Algerian plants.

Algerian Interior Minister Daho Ould Kabila said the 20-odd militants entered the country from nearby Libya in three vehicles, in an operation commanded by extremist mastermind Moktar Belmoktar, who is normally based in Mali.

“The Algerian authorities have expressed, many times, to the Libyan authorities, its fears and asked it a dozen times to be careful and secure borders with Algeria,” Kabila was quoted as saying on the website of the newspaper Echourouk.

The militants made it clear that their attack was fallout from the intervention in Mali. One commander, Oumar Ould Hamaha, said they were now “globalizing the conflict” in revenge for the military assault on Malian soil.

France has encountered fierce resistance from the extremist groups in Mali and failed to persuade many allies to join in the actual combat. The Algeria raid could push other partners to act more decisively in Mali – but could also scare away those who are wary of inviting terrorist attacks back home.