Thirty hostages were killed on Thursday when Algerian forces entered a Sahara Desert gas plant seized by Islamist militants, an Algerian security source told Reuters.

The source said among the dead hostages were eight Algerians, two Japanese, two Britons and one French national. The nationalities of the other dead, and of those who escaped, were not identified.

U.S officials said Wednesday that three Americans were among the hostages and it is still unclear if they were among the 30 dead. The news report added that at least 11 Islamic militants died as well, after forced stormed the plant in an effort to free many dozens of Western and local captives.

The official source said only two of the 11 dead militants were Algerian, including their leader. Taher Ben Cheneb, an Algerian whom the source described as a "prominent jihadist commander" in Sahara.

Troops stormed the gas plant after an operation that appeared to go on for some eight hours, Reuters noted. Algeria refused the kidnappers' demand to leave the country with their hostages, and the kidnappers - who seized control of the facility a little before dawn on Wednesday - demanded that France stop its week-long offense against Islamist rebels in Mali.

The hostages started the attack in retaliation for France's military intervention against al-Qaida-linked rebels in neighboring Mali. The group claiming responsibility is known as both Katibat Moulathamine and the Masked Brigade. The group also calls itself the "Battalion of Blood."

The militants first claimed that they had around 41 hostages, which included seven Americans.

Reuters reported in a previous story on Thursday that 15 hostages were reported to have escaped from Islamist fighters.

Mauritania's ANI news agency reported that one of the kidnappers had claimed two Algerian army helicopters attacked the gas complex, injuring two of the Japanese hostages.