Defence Secretary Leon Panetta said Thursday any US forces that remain in Iraq beyond a year-end deadline would require legal "immunity," despite calls from Iraqi leaders to end the protection.

Asked about a statement from leaders of Iraq's main political parties, Panetta said that "any kind of US presence demands that we protect and provide the appropriate immunity for our soldiers" if there is a post-2011 US mission.

The Pentagon chief's comments, at a news conference in Brussels, exposed a potential sticking point over the legal status of American troops that could derail negotiations underway on a possible future US military force after the end of the year.

After a two-hour meeting hosted by Iraqi President Jalal Talabani, leaders of the country's main political blocs said they agreed on the need for training of Iraqi forces and the purchase military equipment, according to a statement issued by government spokesman Ali al-Dabbagh.

But "the leaders agreed there is no need to give immunity for trainers."

The statement made no mention of how many trainers would be required, for how long or for what specific needs.

About 43,500 US troops remain in Iraq, and all of them must withdraw by the end of the year under a bilateral security accord, which remains in force if no post-2011 deal is agreed.