An internet message purported to be from the militant group led by Abu Musab al-Zarqawi says Egypt's ambassador to Iraq has been killed.
A video on the website showed a blindfolded man who gave his name as Ihab al-Sherif saying he had worked at Egyptian embassies in Iraq and Israel.
Mr Sherif was abducted in Baghdad on Saturday. ID cards bearing his name appeared on a website on Wednesday.
No killing was shown. The authenticity of the claim has not been verified.
A statement released on Wednesday in the name of al-Qaeda in Iraq said Mr Sherif would be killed because he was an "apostate", who had betrayed his faith.
It also criticised the Cairo government for its support of the US and Iraqi administrations.
Al-Qaeda claims to have beheaded several foreign hostages in Iraq under the leadership of Zarqawi, a Jordanian fugitive.
The Egyptian government has not commented on the claim that Mr Sherif has been killed.
A written statement on the website on Thursday said "the verdict of God against the ambassador of the infidels, the ambassador of Egypt, has been carried out".
It said the group had been planning to abduct more foreign envoys in Iraq.
"The reason we delayed the announcement of capturing the ambassador of the dictator Egypt was to be able to capture as many ambassadors as we can," it said.
Mr Sherif had been in Baghdad since early June.