A road sign indicating In Amenas, about 100 km (60 miles) from the Algerian and Libyan border, is seen in this undated picture provided by Norwegian oil company Statoil January 16, 2013. Islamist militants attacked a gas field in Algeria on Wednesday, claiming to have kidnapped up to 41 foreigners including seven Americans during a dawn raid. The In Amenas gas field is operated by a joint venture including BP, Norwegian oil firm Statoil and Algerian state company Sonatrach. REUTERS/Kjetil Alsvik / Statoil/Handout

Washington - Washington was Thursday trying to determine the fate of US hostages caught in the crossfire of an Algerian military rescue bid, and urged its embassies and US businesses to tighten security.

“We are certainly concerned about reports of loss of life. And are seeking clarity from the government of Algeria,” White House spokesman Jay Carney said.

According to a spokesman for the kidnappers, Algerian troops launched an air and ground assault Thursday on a gas complex besieged by Islamists, killing nearly 50 people, most of them hostages.

Britain, France and Norway confirmed an operation was underway at the remote desert site near the Libyan border, which was attacked Wednesday in retaliation for a week-old military campaign against Islamist rebels in neighboring Mali.

But US officials refused to provide any details. “The situation is extremely fluid on the ground,” State Department spokeswoman Victoria Nuland warned reporters, stressing caution was necessary to protect the hostages.

So far the United States has also refused to confirm exactly how many Americans were among those seized during the militants dawn raid on the In Amenas gas field.

“We're not going to get into numbers, we're not going to get into names,” Nuland said. “This goes directly to protecting the safety and security, not only of our Americans but of the other nations that are affected.”

“We are working with the government of Algeria. We're working with other affected nations to try to resolve this situation,” she added.

She stressed however that US embassies and businesses were being asked to look again at their security following the kidnapping and as Washington provides support to French troops fighting Islamist rebels in Mali.

Secretary of State Hillary Clinton “has asked that the security in the entire region be reviewed in light of this,” Nuland said.

There were fears that Al-Qaeda in the Islamic Maghreb (AQIM) which is known to be sheltering in Mali could launch even larger kidnapping operations.

“The AQIM is known for trying to kidnap Westerners. That's how they fund themselves, is through ransoming and that kind of thing,” Nuland said, adding that the Algeria hostage-taking was one of the largest seen in a while.

“So the concern is that groups operating in the region may be trying to do larger-scale operations.” - Sapa-AFP