Abu Laith al-Libi, a leading al-Qaeda member in Afghanistan, has been killed, a website often used Islamist groups said.
The Ekhlaas.org site said on Thursday that al-Libi had "fallen as a martyr", without giving further details.
It was not immediately clear if al-Libi's death was linked to a suspected US missile strike that killed up to 13 foreign fighters in Pakistan's North Waziristan region this week.
The attack had targeted second or third tier al Qaeda leaders, according to residents in the tribal area.
A western official said on Thursday that there are "strong indications" that al-Libi, has been killed.
"Indications are at this point that Abu Laith al-Libi is dead," the official said. "They are very strong indications."
The official, who asked not to be identified, would provide no details on where or how al-Libi was killed.
Tribesmen in in Pakistan's North Waziristan region had said a deputy of al-Libi had been staying there and was among the dead, according to an intelligence official.
Al-Libi, a Libyan, appeared with Ayman al-Zawahri, al Qaeda second-in-command, in a video issued in November to announce that a Libyan Islamist group had joined the organisation.
Islamist websites have carried messages from al-Libi, including one in May in which he said al Qaeda in Afghanistan was willing to exchange prisoners with Britain and other Western countries.