Algerian forces took custody on Friday of a man believed to be one of North Africa's most powerful Islamic terrorists in a highly unusual multinational operation deep in the desert of Niger, according to an official from one of the countries involved.

"From everything we're hearing it is Al Para," the official said, referring to Amari Saifi, a terrorist with ties to Al Qaeda.

Mr. Saifi is known as Al Para because he was trained as a Algerian special forces paratrooper before joining the country's violent fundamentalist Islamic rebellion in the 1990's. He is wanted in connection with many crimes, including his suspected role in the killing of 43 Algerian soldiers and the kidnapping of 32 European hostages, both last year.

Germany paid Mr. Saifi nearly $6 million in ransom for the hostages' release, American and Algerian officials say. He is reported to have used the money to recruit fighters and buy weapons for the Salafist Group for Preaching and Combat, which is fighting to establish an Islamic state in Algeria.

In March, Chadian rebels captured 17 members of the group after a battle near the border with Niger. Mr. Saifi is believed to be among those captured.