Arab League chief Amr Moussa is in Baghdad on what officials have described as a mission to promote national reconciliation.
Mr Moussa, who has not visited Iraq since the invasion in 2003, has previously warned that Iraq is on the verge of civil war.
Mr Moussa was to meet the Iraqi Prime Minister, Ibrahim Jaafari, the Iraqi President, Jalal Talabani, and leading Shi'ite cleric Ayatollah Ali al-Sistani.
The timing of Mr Moussa’s visit had not been announced for security reasons after gunmen attacked League officials in Iraq last month to prepare for today’s visit.
Three police escorts were killed in the attack.
Yesterday, Iraqi security forces arrested a nephew of former president Saddam Hussein in the northern city of Tikrit on suspicion of financing insurgents.
Yasser Sabawi was arrested as residents of Tikrit, Saddam Hussein's home town, protested to mark the beginning of the ousted president's trial on charges of crimes against humanity.
And four US soldiers were killed in two separate bomb attacks north of Baghdad yesterday.
Three soldiers were killed and another was injured in a blast late last night near Balad, 80km north of the capital.
And a US soldier was killed and four were wounded in a roadside bomb near Tikrit.
