KUWAIT -- The family tree of the man suspected of engineering the Sept. 11 attacks reads like a terrorist watch list.
Kuwaiti-born Khalid Shaikh Mohammed is the uncle of convicted 1993 World Trade Center conspirator Ramzi Yousef, a senior Kuwaiti official told reporters Monday.
An older brother is a member of Osama bin Laden's al-Qaida terror network and another brother died in Pakistan when a bomb he was making exploded, the official said.
U.S. officials regard Mohammed as a key al-Qaida lieutenant and organizer of the terror mission that sent hijacked passenger jets crashing into the World Trade Center, the Pentagon and a Pennsylvania field, killing more than 3,000 people.
Mohammed, 37, has not been charged in the Sept. 11 attacks, but he has been charged in a 1995 terror plot. He is one of the FBI's most-wanted terror suspects, and the U.S. government is offering up to $25 million for information leading to his capture.
He is thought to be in or near Afghanistan.
Kuwait, a strong U.S. ally in the Gulf, says Mohammed was Pakistani, although he was born in this oil-rich state. The Kuwaiti official said Yousef was also born in Kuwait.
The official, who spoke on condition of anonymity, did not provide further information on Yousef.
The official said Mohammed's sister is the mother of Yousef, who is serving a life sentence in a U.S. prison in 1993 World Trade Center bombing, which killed six people. Yousef, who was captured in Pakistan in 1995, was also sentenced for a separate attack on an airliner.
U.S. officials say Mohammed, who is just a few years older than Yousef, worked with his nephew on the 1993 bombing plot and a 1995 plan to bomb or hijack U.S.-bound trans-Pacific airliners.
Investigators are looking at the 1993 bombing to see if there are any links with the Sept. 11 attacks.
Mohammed's older brother, Zayed, an al-Qaida member, had "always urged his brothers to work for" the terror network, the Kuwaiti official said.
U.S. counterterrorism officials believe Mohammed joined the anti-Soviet mujahedeen fighters in Afghanistan during the late 1980s. Arabs who helped push Soviet forces from Afghanistan have formed the core of the Islamic militant group that bin Laden both helped fund and fought alongside.
The Kuwaiti official said Mohammed's family traces its roots to Iran and his mother hails from the Pakistani province of Baluchistan.
Mohammed left Kuwait to study in North Carolina, "went straight from America to Afghanistan" and never returned to Kuwait, the official said.
Last week, U.S. officials said they believed he attended Chowan College in Murfreesboro, N.C., before transferring to another U.S. university, where he received an engineering degree.