US-born radical Islamist cleric Anwar al-Awlaki, a key al-Qaeda leader, has been killed in Yemen, the country's defence ministry said.
Unnamed US officials confirmed the reports, but have not provided details.
Awlaki, of Yemeni descent, has been on the run in Yemen since December 2007.
The US had named him a "specially designated global terrorist" for his alleged role in a number of attacks and US President Barack Obama is said to have personally ordered his killing.
The defence ministry statement said only that he died "along with some of his companions".
It gave no further details of his death.
But tribal sources told AFP news agency Awlaki was killed in an air strike in the eastern Marib province, said to be an al-Qaeda stronghold.
An unnamed US official told the Associated Press he was killed by US drone strike. However, the cleric's body was said to be in Yemeni hands.
The death was also announced on Yemeni TV.
BBC security correspondent Gordon Corera says the killing, if confirmed, is significant, because Awlaki is able to reach out to people susceptible to radicalisation through his use of the media.
The reported death comes amid concerns in Washington about the impact of Yemen's political crisis on its ability to go after al-Qaeda militants.
President Ali Abdullah Saleh is facing a widespread protest movement, along with an armed insurrection by renegade army units and tribal fighters.
Mr Saleh, who was injured three months ago when his residence was shelled, returned last week after treatment in Saudi Arabia.
He said in an interview published on Thursday that he will not stand down, as promised in a deal brokered by Gulf States, if his opponents are allowed to stand in elections to succeed him.
Awlaki is described by US officials as a key leader of al-Qaeda in the Arabian Peninsula (AQAP)
He has been implicated in the US army base killings in Fort Hood, Texas, the Christmas 2009 Detroit airline bomb attempt, and a failed bombing in New York's Times Square.
AQAP also claimed to have been behind a plot which sent two bombs in printer cartridges on US-bound cargo planes. They were intercepted in the UK and Dubai.
When he was imam of a San Diego mosque in the 1990s, his sermons were attended by two future 9/11 hijackers, Khalid al-Midhar and Nawaf al-Hazmi.
He also lived in the UK from 2002-04, where he spent several months giving lectures to Muslim youth.
In a video posted in November last year he called for the killing of Americans, saying they were from the "party of devils".
Weeks later, he survived an air strike in Shabwa province in which at least 30 militants were killed.
He has been reported dead in the past following US air strikes on southern Yemen in December 2009 and November 2010. He was the target of a US drone attack that killed two al Qaeda operatives in southern Yemen on 5 May.