Iraq's fiercely anti-US cleric Moqtada al-Sadr has warned that US military trainers will be targets if they stay in the country beyond a year-end deadline for American troops to leave.
The statement from Sadr, whose Mehdi Army militia fought US troops until 2008, follows a deal by Iraqi leaders to allow Prime Minister Nuri al-Maliki to negotiate with the United States on whether to keep trainers in Iraq after the deadline.
Sadr followers have sent mixed messages on that, but any deal to keep US troops in Iraq, even as trainers, remains a sensitive issue in Baghdad and Washington eight years after the U.S. invasion that toppled Saddam Hussein.
"Whoever stays in Iraq will be treated as an unjust invader and should be opposed with military resistance," Sadr said in a statement published on a pro-Sadr website on Saturday.
"A government which agrees for them to stay, even for training, is a weak government."
Sadr's Mehdi Army militia has for the most part demobilised, but US officials say Sadrist splinter groups have continued to attack US troops still stationed in Iraq.
Violence in Iraq has eased sharply since sectarian bloodshed peaked four years ago, but bombings and assassinations are still carried out almost daily by Sunni Islamists, some tied to al Qaeda, and by Shi'ite militas the US government says are backed by Iran.
Sadr himself is now part of mainstream politics and a key ally to Maliki in his fragile power-sharing coalition among Shi'ite, Sunni and Kurdish blocs.
Sadr's representatives walked out of last week's discussions on US troops, signalling possible dissension within the coalition.
US and Iraqi officials agree that Iraq's security forces are capable of taking on internal threats, but say they need training in heavy conventional weaponry like tanks, and in air and naval defences.
Details of any deal are far from clear, and an agreement would need to pass through parliament, say US officials, who want legal immunity for any residual US military presence.
Sadr has in the past threatened to revive his Shi'ite Mehdi Army if US troops stay, but Sadrist sources have said the militia is riven with splinter groups and internal divisions.