Biden's unannounced tour of world hotspots had previously taken him to Kabul, where he met Afghan President Hamid Karzai, and to Islamabad, where he met with top Pakistani officials.

Biden Thursday morning met with the top US commander in Iraq General Lloyd Austin and US ambassador James Jeffrey at the US embassy in Baghdad's highly-fortified 'Green Zone.'

Asked why he's in Iraq, Biden said: "I'm here to help the Iraqis celebrate the progress they made. They formed a government. And that's a good thing. They have a long way to go."

Biden arrived from Pakistan in the Iraqi capital on Wednesday night, according to journalists travelling with him.

The White House said Biden would also meet President Jalal Talabani and Iyad Allawi.