An al-Qaida leader regarded as the terror group's most potent threat to western interests has been killed in Yemen, defence officials in the capital, Sana'a, say.

Anwar al-Awlaki, a dual US-Yemeni citizen, is believed to have been killed at 9.55am on Friday morning at a site 90 miles (140 kilometres) east of Sana'a between the provinces of Marib and al-Jawf in what is believed to have been an air strike. He is thought to have been travelling in a two-car convoy, which local tribal officials say was destroyed.

The CIA and the US military have used drones to target al-Qaida officials in Yemen and had placed Awlaki near the top of a hit list. The US president, Barack Obama, authorised a request to target Awlaki in April last year, making him the first US citizen to be a legal target for assassination in the post-9/11 years

The US embassy in Sana'a declined to comment on the reports of Awlaki's death, fuelling speculation that the CIA had indeed got its man. Yemeni officials said they were not yet sure who had killed him.

However, they released details of the killing within several hours of it happening, suggesting that Sana'a was either directly involved or well-briefed by the US.

Awlaki is credited with inspiring or directing at least four plots on US soil in recent years – a shooting inside the Fort Hood military base, the failed Times Square bombing, the failed underwear bomber and a parcel bomb hidden inside a printer that also failed to explode while inside a passenger jet.

He is thought to have been the leader of the foreign operations unit inside the al-Qaida in the Arabian Peninsula group, which has in recent years taken centre stage in the global jihad campaign inspired by Osama bin Laden.

Awlaki was born in the US state of New Mexico in 1971 to Yemeni parents who took him back to Yemen after early childhood. He returned to the US in 1991 to attend college. US authorities believe he came into contact with at least two of the 9/11 hijackers while giving sermons at a San Diego mosque.

His fingerprints are also all over failed plots to target British and European interests. The attempted murder of the MP Stephen Timms was inspired by Awlaki's sermons and a British Airways employee, Rajib Karim, was convicted in February of plotting attacks against the airline.

The death of Awlaki is the most significant blow to the al-Qaida organisation since Bin Laden was assassinated in May. He was one of the few senior operatives orientated to western ways and in recent years had become increasingly strident in his calls for Muslims to wage jihad against the US.

His firebrand rhetoric had become renowned on jihadi websites and is thought to have inspired many more followers. With a blog, a Facebook page and numerous YouTube videos of his sermons, he had increasingly been regarded by the US National Security Council as one of the most dangerous men alive.