, a Saudi citizen whose real name is Abdul Mohsen Adballah Ibrahim al Charekh, was the highest-ranking member of the Khorasan Group
-- a collection of veteran al Qaeda jihadis which had moved into Syria, the Pentagon said in a statement
He was killed in an airstrike in northwest Syria on Thursday, the statement said.
Nasr, who was once al Qaeda's chief financial officer and had been designated a Specially Designated Global Terrorist by the U.S. Treasury, is the fifth senior Khorasan Group leader killed in the last four months, said the statement.
"The United States will not relent in its mission to degrade, disrupt and destroy al-Qaeda and its remnants," said Secretary of Defense Ash Carter.
"This operation deals a significant blow to the Khorasan Group's plans to attack the United States and our allies, and once again proves that those who seek to do us harm are not beyond our reach."
Nasr's death was referred to widely on jihadist social media sites, where he was mourned as a martyr.
Nasr had played a significant role in the group's finances and had also been instrumental in organizing routes for new recruits to travel, via Turkey, from Pakistan to Syria, the Pentagon said.
"Al-Nasr was a longtime jihadist experienced in funneling money and fighters for al-Qaeda. He moved funds from donors in the Gulf region into Iraq and then to al-Qaeda leaders from Pakistan to Syria," the Pentagon spokesman said in a statement.
CNN terrorism analyst Paul Cruickshank said the death of Nasr represented a "significant blow to al Qaeda," as he was one of the terror group's most senior figures in Syria.
"He was a highly influential strategist and prolific online propagandist and previously played key operational roles for the terrorist organization in the Afghanistan-Pakistan border region and Iran, including a stint in 2012 as al Qaeda's chief financial officer," he said.
Since relocating to Syria in 2013, he had become a leading figure in the al Nusra Front
, an al Qaeda affiliate, said Cruickshank.
"He is believed to have worked to ensure the group remained within al Qaeda's orbit and is also believed to have worked closely with deceased Khorasan Group leader Muhsin al Fadhli," he said.
Fadhli, a Kuwaiti-born jihadi, was killed in a strike in Syria in July
What is the Khorasan Group?
Khorasan's existence wasn't publicly acknowledged in the U.S. until last year, when U.S. director of national intelligence James Clapper said it was operating in Iraq and Syria with a focus on exporting terror to the West.
The Khorasan Group has actively plotted against U.S. and other Western targets, a senior U.S. official has said.
Former leader Fadhli fought alongside al Qaeda and the Taliban in Afghanistan and was among the few trusted al Qaeda leaders who received advance notification of the September 11 attacks, according to the Pentagon.