They first turned to a secret fund that the Central Intelligence Agency bankrolled with monthly cash deliveries to the presidential palace in Kabul, according to several Afghan officials involved in the episode. The Afghan government, they said, had already squirreled away about $1 million from that fund.

Within weeks, that money and $4 million more provided from other countries was handed over to Al Qaeda, replenishing its coffers after a relentless C.I.A. campaign of drone strikes in Pakistan had decimated the militant network's upper ranks.

"God blessed us with a good amount of money this month," Atiyah Abd al-Rahman, the group's general manager, wrote in a letter to Osama bin Laden in June 2010, noting that the cash would be used for weapons and other operational needs.