The airport shuttle driver accused of plotting a bombing in New York had contacts with Al Qaeda that went nearly all the way to the top, to an Usama bin Laden confidant believed to be the terrorist group's leader in Afghanistan, U.S. intelligence officials told The Associated Press.

Mustafa Abu al-Yazid, an Egyptian reputed to be one of the founders of the terrorist network, used a middleman to contact Afghan immigrant Najibullah Zazi as the 24-year-old man hatched a plot to use homemade backpack bombs, perhaps on the city's mass transit system, the two intelligence officials said.

Intelligence officials declined to discuss the nature of the contact or whether al-Yazid contacted Zazi to offer simple encouragement or help with the bombing plot prosecutors say Zazi was pursuing.

Al-Yazid's contact with Zazi indicates that Al Qaeda leadership took an intense interest in what U.S. officials have called one of the most serious terrorism threats crafted on U.S. soil since the 9/11 attacks.

"Zazi working with the Al Qaeda core is exceptionally alarming," said Daniel Bynam of the Brookings Institution's Saban Center. "The Al Qaeda core is capable of far more effective terrorist attacks than jihadist terrorists acting on their own, and coordination with the core also enables bin Laden to choose the timing to maximize the benefit to his organization."

U.S. intelligence officials said earlier that Zazi had contact with an unnamed senior Al Qaeda operative. That helped distinguish Zazi from other would-be terrorists who have acted on their own in planning or attempting U.S. attacks.

The officials, speaking on the condition of anonymity because the case remains under investigation, declined to describe al-Yazid's specific interaction with Zazi, who has pleaded not guilty to conspiring to use weapons of mass destruction. But one senior U.S. intelligence official said the contact between Zazi and the senior Al Qaeda leader occurred through an intermediary.

Just weeks before U.S. intelligence officials identified Zazi as a possible terrorist threat in late August, John Brennan, President Barack Obama's top domestic terrorism adviser, told a Washington audience that "another attack on the U.S. homeland remains the top priority for the Al Qaeda senior leadership."

U.S. intelligence officials and prosecutors have said that Zazi was recruited and trained by Al Qaeda. They say he and others traveled last year to Pakistan to receive the training.

Prosecutors say Zazi, during meetings with federal investigators before his arrest last month, "admitted that he received instructions from Al Qaeda operatives on subjects such as weapons and explosives" during his trip to Pakistan.

Arthur Folsom, Zazi's Denver lawyer, said Wednesday he was not aware of a claim that his client had contact with al-Yazid or any other senior Al Qaeda leader. He said Zazi told investigators he met with a number of people while in Pakistan.

"He may well have talked to someone at a coffee shop who had some type of connection he wasn't aware of," Folsom said. "Under those grounds, guess what? I have a connection to Al Qaeda and so do you."

Folsom said prosecutors have mischaracterized comments Zazi made after he voluntarily agreed to meet before his arrest last month. Folsom said those comments have "been wildly exaggerated or blown out of proportion."

Folsom said Zazi never said he visited a training camp or received explosive training from Al Qaeda. Folsom said he doesn't know who the government claims his client contacted who may have had Al Qaeda connections.

"They either don't know or won't say who this person is," Folsom said, referring to prosecutors. "It's hard for us to comment on this because we don't know who this person is."

Folsom said he was in New York meeting with prosecutors and investigators over the weekend and that was not mentioned.

Zazi, who is being held without bond in New York while awaiting trial, has denied receiving Al Qaeda training or visiting one of the group's training camps. He said before his arrest that he traveled to Pakistan to see his wife, who lives in Peshawar.

In court documents, prosecutors say Zazi is linked to three e-mail accounts that he used to pursue his bomb plot. Investigators say they found nine pages of handwritten bomb-making instructions when searching two of the e-mail accounts. The notes were sent to the e-mail accounts while Zazi was in Pakistan last year, prosecutors say.

The bomb, which can be made of hydrogen peroxide and flour, is similar to the explosives used by terrorists in the 2005 London subway bombings that killed 52 people.

Prosecutors say Zazi accessed the bomb-making instructions and downloaded them on to his computer after moving to the Denver area in January. In a Colorado hotel suite in early September, Zazi contacted someone "on multiple occasions" for help correcting mixtures of bomb ingredients, "each communication more urgent in tone than the last," court papers say.

Al-Yazid, 53, also known as Abu Saeed al-Masri and Sheikh Said, is a well-known Al Qaeda figure who initially disagreed with bin Laden's 9/11 plot, according to the 9/11 Commission Report. Al-Yazid was known at the time of the attack as head of Al Qaeda's finance committee.

He proclaimed in a June interview with Al-Jazeera television that Al Qaeda would use nuclear weapons in its fight against the United States.

A member of Egypt's radical Islamist movement, al-Yazid took part in the 1981 assassination of President Anwar Sadat, according to "In the Graveyard of Empires," a book by counterterrorism expert Seth G. Jones. He spent three years in prison, where he joined Ayman al-Zawahiri's Egyptian Islamic Jihad, Jones wrote. al-Zawahiri is considered Al Qaeda's No. 2 leader, behind Usama bin Laden.

Al-Yazid left Egypt for Afghanistan in 1988 and later moved to Sudan in 1991 with bin Laden, serving as his accountant. Al-Yazid returned to Afghanistan in 1996 and became a confidant of bin Laden and a member of its Shura Council, according to Jones.

In 2007, al-Yazid took over Al Qaeda operations in Afghanistan.

He was reported killed last year in clashes with Pakistani forces near the Afghan border in August 2008 but re-emerged to the surprise of counterterrorism officials.

Terrorism experts say al-Yazid's contact with Zazi in the foiled New York City bombing plot underscores the seriousness of the threat.

"I think that it would suggest the Zazi was taken seriously by Al Qaeda, and that they wanted him to feel encouraged and supported," said Charles S. Faddis, who headed the weapons of mass destruction unit at the CIA's Counterterrorism Center until he retired in May 2008.

"It may also have meant that they were attempting to determine to what extent he represented an opportunity to do something inside the United States," said Faddis, who also ran operations against Al Qaeda. "For instance, they may have been trying to figure out if they were looking only at an individual or at someone who represented a larger group of jihadists."