Al-Sadr has been angry with the US since its invasion of his country in 2003. Many share his sentiments and he has a large group of followers.
"Al Sadr is known as the only political leader who objected to the presence of the US in Iraq since 2003,” says Sami Rasouli, who works for the American Iraqi Reconciliation Project. Last Friday he witnessed a large anti-American demonstration. “Sadr chanted with thousands of his followers, that the US should be out of Iraq.”
Currently, there are 4,083 US troops in different places in Iraq.
“We agreed for the United States to bolster the Iraqi efforts to isolate and pressure Mosul by deploying 560 additional troops in support of the Iraqi Security Forces [ISF],” announced US Defense Secretary Ashton last week.
“These additional US forces ... will bring unique capabilities to the campaign and provide critical support to Iraqi forces,” indicating that an attack on the biggest Islamic State stronghold in Iraq may be imminent.
Sadr, by declaring that US troops "are a target for us" has excluded any cooperation in the struggle against the Islamic State, although he and other Shia leaders oppose the Sunni-Muslim group.
al-Sadr chanted with thousands of his followers, that the US should be out of Iraq
“A great divisive question in Iraq and Syria was that the Americans are looking to defeat the Islamic State but they don't want to benefit the Shia fundamentalist movement, Al Sadr or Iran,” says author and journalist Patrick Cockburn. “Although [al-Sadr] is not close to the Iranians.”
But in practice, the combat situation on the ground may be complex and confusing. “The Americans said they won't bomb when Shia militia is attacking the Islamic State. In fact they have done so, so it is 'now you see it, now you don't',” says Cockburn.
Meanwhile, al-Sadr is not the most powerful Shia in Iraq at this moment. This is the Grand Ayatollah Al al-Sistani and he’s had his differences with al-Sadr.
“In 2004, when al-Sadr raised the Mehdi army and fought the Americans, Sistani was very much against it, he left Najaf during the battle, he didn't want a confrontation with the Americans,” says Cockburn.
“Since the relations have gotten much better and al-Sadr wants to sort of keep in with the rest of the religious hierarchy, so there is friction at times but a much better relationship than it used to be.”
But where they still differ is the amount of interference in public and political life. Al-Sadr led thousands into Bagdad’s Green Zone earlier this year and has organised massive protests against alleged corruption in the government of Prime Minister Haider al-Abadi.
“Sistani's always had a different attitude, the Iranian one is that clergy should play a public role in controling the state,” explains Cockburn.
“Sistani and the Shia religious leadership have always taken a different line in that the clergy should be a moral influence but they shouldn't take direct control of the state. Because they themselves would then be contaminated by its corruption.”
And that is where al-Sadr plays a much more political role, profiling himself as a leader who actively fights corruption and the American presence in Iraq.
So the more troops Washington sends, the more problems it can expect from Moqtada al-Sadr.