Nabhan is believed to have been hiding in Somalia in recent months
Saleh Ali Saleh Nabhan, a top al-Qaeda suspect, has been on the FBI's wanted list for years.
He was killed in an attack by US forces in southern Somalia on 14 September, a US official says.
The 28-year-old Kenyan is wanted in connection with the 2002 attacks on a hotel and an Israeli airliner in his home city of Mombasa.
Some reports suggest he was also involved in the 1998 bombings of the US embassies in Kenya and Tanzania in which more than 250 people died.
Nabhan was reportedly one of the original members of the al-Qaeda East Africa cell.
The BBC's Odhiambo Joseph in Mombasa says Nabhan grew up in the 1980s in Mombasa's Majengo slum, an area inhabited at the time by Swahili Arabs.
After dropping out of secondary school, he attended a local Koranic school, or madrasa, in Majengo.
Residents say he then went to work in the Middle East in the mid-1990s.
His mother Aisha Abdallah told the BBC he then returned home and was selling fruit juice and mobile phone accessories before he disappeared in 2002, leaving behind a nine-month-old daughter.
Shortly afterwards, his name became infamous - on the day of the Mombasa attacks.
He is believed to have owned the vehicle used in the attack on the Israeli-owned hotel near Mombasa that killed 15 people.
He is also wanted by the FBI in connection with a botched missile attack on an Israeli airliner in Mombasa on the same day.
Our reporter says many of his family - who were picked up and questioned after the attack - have moved from Mombasa further up the coast to Lamu Island and his ancestral home of Malindi.
According to Andre le Sage, from the African Centre at the National Defense University in Washington DC, Nabhan has probably been one of the individuals who has maintained overall operational command in East Africa with "possibly even connections to al-Qaeda senior leadership in the Pakistan-Afghanistan area".
"If he was removed from the East Africa al-Qaeda cell, it would certainly degrade the capabilities of that network and their ability to conduct future attacks," he told the BBC's Network Africa programme.
A local Muslim leader told the BBC that since 2002, Nabhan has made several visits to Malindi.
He says he evaded capture in August last year, when Kenya police launched a raid in the coastal town for his associate Fazul Abdullah Mohammed, the alleged mastermind of the East Africa embassy bombings.
Mr Mohammed was reported to have gained entry to Kenya through Lamu Island, which borders Somalia.
Nabhan - alongside other al-Qaeda-linked foreign suspects like Mr Mohammed - has reportedly been hiding in Islamist-held areas of Somalia for some time.
He is said to have been killed in a helicopter raid by US special forces on the coastal town of Barawe, which is under the control of the Islamist group, al-Shabab.
Mr le Sage says Nabhan has been working closely with al-Shabab "in the management of training camps, particularly training camps where foreign fighters were receiving jihadist training".
But while he says his removal will have an impact on both al-Qaeda and al-Shabab, it will not have larger political implications in Somalia.
"Al-Shabab network is composed of many leaders and many individuals, Nabhan was an important character but al-Shabab will be able to bring up other leaders to replace him or fill his shoes."
Last year, one of al-Shabab's main leaders Aden Hashi Ayro, who reportedly trained in Afghanistan, was killed in a US air strike.
Since then analysts say the Islamists, boosted by foreign fighters, have gained ground in their fight against the UN-backed government.