UPDATE THURSDAY 17:30 EST:
Between six and 34 foreign hostages were killed on Thursday in a conflict between militants who had seiged a BP oil field and the Algerian military.
Several Western hostages were killed by an Algerian helicopter strike.
A British security source told CBS News "the Algerians were firing from helicopters at anything that moved."
The militants want to leave the country with the remaining hostages to use them as a bargaining tool. Algeria refuses to negotiate.
At 17:15 EST, Al Arabiya reports that the Algerian army controls part of hostage site, but the gas facility still surrounded.
British Prime Minister Cameron told Algeria's Prime Minister Abdelmalek Sellal he was "extremely concerned" about the "very grave and serious situation." Japan has asked Algeria to immediately stop operations that are "endangering hostages' lives."
A man identifying himself as a Japanese hostage told Al Jazeera that he and a Norwegian hostage had been wounded by Algerian sniper fire. A French national told France24 that the hostages have been forced to wear explosive belts and that the militants are heavily armed.
The U.S. is largely in the dark despite sending a quick response force to the area on Wednesday night. A senior U.S. official told Raddatz around 09:00 EST that they're "trying to get clarity but just don't know anything for sure."
The hostage situation began on Wednesday when at least 20 jihadists raided the In Amenas oil field 60 miles away from the Algeria-Libya border, killing two foreigners and kidnapping between 20 and 41 foreign hostages from countries including the U.S., UK, France, Romania, Ireland, Malaysia, Japan and Norway.
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