A reporter travelling with Biden confirmed that mortars had landed in the Green Zone and said that Biden was "fine".

Biden was to hold talks with Iraqi politicians and meet American troops on his third trip to Iraq this year.

Biden said he was in Baghdad to help "resolve outstanding political issues" so that Iraq would be "more stable" when US forces leave the country in 2011.

He said he had twice been asked by Iraqi leaders "to act as an interlocutor" as they work through political issues.

Election

He mentioned the elections law in particular.

"A successful election is the necessary condition for some of the outstanding political issues to be resolved," Biden said.

The US administration is anxious to resolve long-standing disputes between Kurdish, Shia and Sunni communities over land and oil that US officials fear could yet rip apart the country.

Biden said a national election in January was the key to resolving those tensions.

The White House said earlier that Biden would meet Jalal Talabani, the Iraqi president, and Nouri al-Maliki, the prime minister, and other senior leaders in Baghdad and "convey the strong US commitment to Iraq's future and national unity".

There are currently about 130,000 US troops in Iraq.

The US is to withdraw all combat forces by the end of August 2010 and fully withdraw the remaining 50,000 troops by the end of 2011 as part of a security agreement signed between the two countries.