Iraqi National Congress leader Ahmed Chalabi says he has escaped an assassination attempt which has left two of his bodyguards wounded.
Mr Chalabi was returning from Najaf after meeting Ayatollah Sistani
He was travelling from Najaf to Baghdad when the attack happened, he said.
"A car started following us and opened fire on our convoy," former Pentagon favourite Mr Chalabi told reporters.
Also in the Iraqi capital, mortar fire hit the heavily-fortified zone where the first meeting of Iraq's interim parliament was due to be held.
One Iraqi was wounded in the attack.
Members of the 100-seat assembly had gathered inside the Green Zone compound ahead of the four-day session.
An hour later, a second series of explosions was heard by delegates inside the chamber. It was not immediately clear what caused the
Members are expected to elect a president, two vice-presidents and other officials. Assembly members will also be sworn in.
They are to advise the interim government as it prepares for elections early next year.
Late on Tuesday, gunmen killed three Iraqi women who worked at a US military base in Mosul.
This was the latest in a series targeting Iraqis seen as collaborators with the Americans.
Mr Chalabi said he had been to Najaf to meet Ayatollah Ali al-Sistani, Iraq's most prominent cleric.
"Two of my bodyguards were wounded, one of them seriously," he said.
Mr Chalabi, a member of Iraq's interim national assembly, was on his way to attend the assembly's first meeting in Baghdad.
"It was an ambush. I don't think there is anything further to say. These things are part of the job."
The attack took place in Latifiya, a town south of Baghdad, where gunmen have fired on several foreigners and Iraqi officials in the past.
Mr Chalabi returned to Iraq earlier this month after a warrant was issued for his arrest on counterfeiting charges. It is not clear why the authorities have not arrested him to date.