An influential Sunni group in Iraq, the Association of Muslim Scholars, has criticised the government's amnesty offer for insurgents.
The amnesty is meant to win over insurgents to the political process
One of the group's leaders, Muthanna Harith al-Dari, said it was no more than a public relations exercise.
He said so many groups were excluded from the amnesty that it was meaningless, and most armed groups had already rejected it.
The government has insisted that it has got a positive response to its offer.
Officials have said the government is already in talks with some groups. But it has refused to say who it is talking to.
It says anyone who has been involved in criminality, or has killed American troops or Iraqis will not be able to take advantage of the amnesty.
The plan, which Prime Minister Nouri Maliki presented to parliament on Sunday, aims to stem sectarian violence by offering an amnesty to some insurgents.
"Neither the principal armed groups of resistance nor political organisations like ours have accepted this plan which ignores a timetable for the withdrawal of foreign troops," Mr Dari said.
He insisted that the groups mentioned in media reports as having taken up the amnesty were absolutely unknown.