The anti-US Shia cleric Moqtada Sadr is back in Iraq after years of self-imposed exile, officials have said.
After spending more than three years in Iran, the radical cleric returned to Najaf, his stronghold south of Baghdad.
The militia he founded, the Mehdi Army, clashed several times with US and Iraqi forces after the 2003 US-led invasion.
Last month, his political movement secured a deal to be part of the new government, with 39 parliamentary seats and seven ministries.
Meanwhile, the new Iranian acting Foreign Minister, Ali Akbar Salehi, has become the first senior official from Tehran to visit Baghdad since the formation of the new Iraqi government in December.
Mr Salehi held talks with his Iraqi counterpart, Hoshyar Zebari, as well as Prime Minister Nouri al-Maliki. Both sides stressed the need to develop good relations.
The visit comes as the US prepares to withdraw its 50,000 military personnel still in the country by the end of the year.