In Washington, a Western official who asked not to be identified said there were "very strong indications" that Libi had been killed. But he provided no further details.
The reports follow a missile strike late on Monday in the Pakistani tribal area of north Waziristan that was reported to have killed more than 10 militants.
Al-Ekhlaas, an al Qaeda-affiliated forum, announced the death of Libi, who has appeared in the past in al Qaeda videos, Site said, referring to media reports that he had been killed in a US air strike.
"As the banner was posted on Ekhlaas by a webmaster of the forum, it seems as if the announcement of his death has been confirmed to the forum administrators," Site said, without elaborating.
In Afghanistan, Nato-led forces said they had no information on whether the Libyan militant had been killed.
And Pakistani interior ministry spokesman Brigadier Javed Cheema told AFP: "We have no information of his killing."
A US official in Washington said that "taking down any of these guys can have both an operational and symbolic impact. The pressure is on. They got to know it. Nobody's giving up on this fight."
Security officials in Pakistan said earlier on Thursday that a clutch of al Qaeda militants, including seven Arabs and six Central Asians, were killed when a suspected US missile hit their hideout, a house in the troubled tribal district of North Waziristan, late on Monday.

Copyright AFP (Agence France-Presse), 2008