Islamist militants seized foreign nationals Wednesday at an Algerian gas field operated by two Western energy majors, fanning fears that France 's military operations in Mali are sparking a terrorist backlash in neighboring countries.

A group of about 40 al Qaeda militants attacked the In-Amenas gas field in east-central Algeria, along the Libyan border, at about 2 a.m. local time, according to an Algerian energy worker who was briefed on developments by colleagues at the scene.

The militants killed three people during the attack and are entrenched in the base with at least six hostages, four Japanese, one French and one British, after it was surrounded by Algerian armed forces, the person said. All Algerian nationals were let go, he said.

As of early afternoon Wednesday, the standoff was still underway, he said.

A
U.K. government spokesman said that "a terrorist incident is ongoing" near In-Amenas operated by BP PLC (BP, BP.LN), Norway 's Statoil ASA (STL.OS, STO) and the Algerian energy company Sonatrach. "The British embassy in Algiers is aware of the incident and liaising with the local authorities."

He said the government is "urgently seeking clarification from oil companies working in the area."
France 's Foreign Ministry is working on confirming reports about the attack, said a spokesman.

There was confusion as to the exact number of casualties and hostages.

The Associated Press reported that at least eight foreigners, including Norwegian and Japanese nationals, were seized.
Algeria 's state news service APS said two people were killed and six injured in the attack.

Ireland 's foreign minister Eamon Gilmore issued a statement calling for the immediate release of an Irish citizen "who is reported to have been among the group of oil workers kidnapped in Algerian this morning."

Statoil, which employs fewer than 20 people at the site, 10 of them Norwegians, also said there has been an attack against the gas facility. It said it was in contact with the families of its employees but didn't elaborate on their situation.

A spokesman for
Japan 's foreign ministry said it was "aware of the report," and gathering information.

A Sonatrach spokeswoman said the company couldn't immediately comment on the situation in In- Amenas.

In Amenas harbors nearly 50 crude as well as gas fields, linked to the northern coast through several pipelines.

Last Friday, French military forces joined Malian troops battling Islamist rebels in the West African nation, amid Western fears that insurgent groups with links to al Qaeda could destabilize the region and gain the ability to strike overseas.

French officials have said they feared the campaign could lead jihadist movements to target French and European interests in retaliation.

Since the start of
France 's military intervention in Mali , Algeria has displayed unexpected support to the French campaign.

Algeria, which has traditionally championed a non-interventionist policy and had voiced reservations about any foreign military role in Mali, allowed French combat jets to fly through its airspace and announced on Monday that it would close its southern border with Mali.

France's President Francois Hollande repeated on Tuesday that closing the border was an important step to prevent al-Qaeda militants, many of whom are Algerian nationals, and have build up strongholds in Mali's north, from seeking refuge in Algeria's part of the vast Sahara desert.

Analysts said they were skeptical that
Algeria , although the mightiest military force in the region, would succeed in fully tightening the border.

"It's possible to reinforce control on that border, but closing it is virtually impossible," said analyst Mohamed Chafik Mesbah, a retired officer of the Algerian army.
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