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Sources: Top al Qaeda figure hiding in Pakistan

WASHINGTON (CNN) -- Abu Zubaydah, the elusive 30-year-old Palestinian believed to be operational commander of al Qaeda, is hiding in Pakistan, knowledgeable sources said Thursday.

"There's evidence of that," said one source.

U.S. officials describe Zubaydah as one of Osama bin Laden's key lieutenants, well connected with terrorist sleeper cells around the world, who may seek to organize additional attacks against U.S. targets.

Officials said the suspect's full name is Zayn al-Abidn Muhammed Hasayn Abu Zubaydah. Born in Saudi Arabia, he speaks English and is considered an expert at disguises, skilled at remaining out of sight for years at a time.

Reacting to reports from Iran that 150 al Qaeda and Taliban members have been arrested there after crossing the border from Pakistan, U.S. officials said they believe the number is exaggerated, though some al Qaeda and Taliban have crossed into Iran.

The United States has given Iran information about some of them, officials say. U.S. and Iranian officials have said they do not believe any senior al Qaeda officials are in Iran.

As for bin Laden himself, despite persistent rumors he could be in Pakistan or even Iran, U.S. officials said their best evidence indicates he is still in Afghanistan.