US insists on immunity for troops in Iraq after 2011
US defence secretary Leon Panetta has insisted that any US troops remaining in Iraq beyond the scheduled pull-out at the end of this year must remain immune from local prosecution.
Talks are continuing for several thousand of the 43,000 US troops to remain to train Iraqi forces.
The Iraqi government says immunity is not necessary.
However, Mr Panetta insisted that "we protect and provide the appropriate immunity for our soldiers".
All American troops are scheduled to leave by the end of the year and an agreement is needed for the trainers to remain.
Iraqi political figures met on Tuesday night and agreed that while the trainers were needed, they should not have immunity from prosecution.
Government spokesman Ali al-Dabbagh said: "Immunity is the main disputed point. If we do not have agreement on the immunity, there will be no agreement on the number."
Many Iraqis are especially sensitive about the issue, given the number of civilian shootings involving US troops since the US-led invasion.
Private contractors have already lost their immunity.
But Mr Panetta, visiting Brussels, said: "I can say very clearly that any kind of US presence [in Iraq] demands that we protect and provide the appropriate immunity for our soldiers."
He added: "These issues are still very much in negotiation."