ALGIERS, Algeria — A deadly Algerian military raid to free hostages from at least 10 countries and wipe out their Islamist militant captors moved closer to the heart of the natural gas complex on Friday, the government news service said.

A total of 18 militants were killed and the plant's living quarters were secured, according to the news agency, which cited security officials. Dozens of energy workers remained unaccounted for after the Algerian military's initial claim that the assault at the remote desert facility was over late Thursday.

Algeria's government has kept a tight grip on information, but it was clear that the militant assault that began Wednesday has killed at least six people from the factory — and perhaps many more.