WASHINGTON - Osama bin Laden is hiding in a remote tribal area along Afghanistan's 1,500-mile border with Pakistan, separated from his top deputy and, in a sign he has to be careful about whom he trusts, surrounded by fellow Arabs.

His No. 2, Ayman al-Zawahri, is hiding in a more settled area along the border, surrounded by al-Qaida operatives of his Egyptian nationality, according to U.S. intelligence officials familiar with his pursuit.

Their separation has opened a debate in national security circles in the United States and elsewhere about whether the leaders have split up. Neither man mentions the other by name in public pronouncements, and both headed separate groups before joining forces in 1998.

Al-Zawahri has decided to take a more prominent public role than has bin Laden, releasing dozens of written and recorded Internet messages, including a video this month urging Muslims to support Iraqi insurgents.

On Sunday, bin Laden was heard in his first new message in three months, purportedly saying the West was at war with Islam and calling on his followers to go to Sudan to fight a proposed U.N. force in Darfur.