Somali police have said Fazul Abdullah Mohammed, one of Africa's most wanted al-Qaeda operative, was killed in Mogadishu, Somalia's capital city, earlier this week.
US Secretary of State Hillary Clinton said on Saturday that the death of Mohammed, to whom she referred as "Harun Fazul", was "a significant blow to al-Qaeda and its extremist allies and its operations in East Africa".
"It is a just end for a terrorist who brought so much death and pain to so many innocents in Nairobi and Dar es Salaam and elsewhere - Tanzanians, Kenyans, Somalis and our own embassy personnel," Clinton said during her tour of Africa.
Halima Aden, a senior Somali national security officer, told the Reuters news agency that Mohammed was killed at a police checkpoint "this week".
"He had a fake South African passport and of course other documents. After thorough investigation, we confirmed it was him, and then we buried his corpse," Aden said.
"He was killed on Tuesday midnight in the southern suburbs of Mogadishu at Ex-control police checkpoint. Another Somali armed man was driving him in a four-wheel drive when he accidentally drove up to the checkpoint," he said.
"We had his pictures and so we cross-checked with his face. He had thousands of dollars. He also had a laptop and a modified AK-47."
Nicholas Kamwende, head of the Anti-Terrorism Police Unit in Somalia's neighbour Kenya, also told Reuters that the unit too had been informed by US embassy sources of Mohammed's death.
"We received intelligence from within the US embassy that [Mohammed] is dead. We ourselves do not yet have any evidence of his death," Kamwende said in Nairobi, the Kenyan capital.
'The big one'
The Comoros-born Fazul Abdullah Mohammed was one of the most dangerous al-Qaeda operatives active in East Africa.
He was suspected of masterminding the 1998 US embassy bombings there. More than 220 people died and 5,000 were hurt in the attacks, which were al-Qaeda's first major hit on US targets.
David Shinn, a professor of international affairs at George Washington University, said Mohammed has been "the leader of Al-Qaeda in East Africa for the last 10 years or so".
"The US has been trying to track him down together with [his] two colleagues for more than 10 years. The two colleagues were killed earlier: one by Ethiopian troops inside Somalia in 2007, the other by US special forces in south Mogadishu in 2009," Shinn told Al Jazeera.
"He was the last of three and he was the big one."
The US FBI has described him as fluent in five languages and a master of disguise, forgery and bomb making. It lists him as one of its most wanted men with a $5m bounty.
Al Jazeera's Imran Garda reported from Washington that Hillary Clinton's reference to him as "Harun Fazul" alludes to the fact that he had many aliases.
The Al-Shabab link
A senior commander of al-Shabab, Somalia's al-Qaeda-linked fighter group, had previously told the AFP news agency that Mohammed was one of the two killed in an attack in Mogadishu last Wednesday.
"One of the men that was killed near Mogadishu was Fazul Abdullah, may Allah bless his soul," the unnamed leader said.
"He is not dead as thousands like him are still in the fight against the enemy of Allah."
George Washington University's David Shinn said "the fact that [Mohammed] was killed in Mogadishu implies that there is perhaps an even closer connection between al-Shabab and al-Qaeda than we are aware of".
"We know there are close links but this would suggest that there may be material support going on at the present time," Shinn said.
While al-Qaeda has been marginalised in East Africa for lack of major success since the 2001 bombing of a hotel in Kenya, al-Shabab has made much progress on its own inside Somalia, he warned.
Somali police have warned Mogadishu residents of attacks by al-Shabab rebels who, security forces said, may take advantage by carrying out hits.
The Horn of Africa country has been rocked by two days of protests, with demonstrators protesting a deal to extend the mandates of the incumbent president and parliament.
One recent act of violence occurred on Friday, when the Somali interior minister was killed in a suicide bombing that was allegedly carried out by the bureaucrat's relative.
One of al-Shabab's stated objectives is to implement its own strict interpretation of Islamic law, or sharia, in Somalia.
Somalia has been without an effective central government since the overthrow of a dictator in 1991.