US Vice President Joe Biden said on Wednesday the United States and Iraq are embarking on a new phase in their ties after Washington kept its promise to pull all of its troops out of the country.

Biden, President Barack Obama's point man on Iraq, was speaking a day after arriving on a surprise eighth visit to Baghdad since he took office, a trip that follows a bloody seven days in which at least 61 Iraqis were killed.

"Our troops... are leaving Iraq and we are embarking on a new path together, a new phase in this relationship... between two sovereign nations," Biden said at the opening of a meeting of the US-Iraq Higher Coordinating Committee.

"That partnership includes a robust security relationship, based on what... you think that relationship should be."

Biden's trip, which was not previously announced by the White House, comes ahead of a December 31 deadline for the withdrawal of US troops from Iraq, which at their peak numbered 170,000 in 2007.

Speaking before the committee alongside Iraqi Prime Minister Nuri al-Maliki, Biden said that Washington had kept its promise to pull out all of its soldiers on schedule.

He said the committee would be the centrepiece of US and Iraqi efforts to build their relationship, notably in security issues such as training, intelligence and counter-terrorism.

"We kept our promise to withdraw from Iraq's cities in 2009. We kept our promise to end our combat mission in the summer of 2010," said the US vice president.

"And now, we are keeping our promise we made back in 2008 to remove our troops from Iraq by the end of this year, and they will be removed.

"Drawing down our forces is not only in the best interest of Iraq, but it's in the best interest of the United States of America as well, and the best interest of the relationship.

"In one month, our troops will have left Iraq, but our close strategic partnership ... will, God willing, continue," Biden said.

The American leader was accompanied by US ambassador James Jeffrey, General Lloyd Austin, the US military's top commander in Iraq, and Deputy Energy Secretary Dan Poneman.

Besides Prime Minister Maliki, he is also due to meet President Jalal Talabani and parliament speaker Osama al-Nujaifi.

In a statement issued as he arrived in Baghdad, the White House said Biden's visit was aimed at "deepening our cooperation on politics and diplomacy; trade and finance; energy... and defence and security," along with other fields.

Obama on October 21 announced that US troops would leave Iraq by the end of 2011, bringing to a close an almost nine-year war that has left thousands of US soldiers and tens of thousands of Iraqis dead, and cost hundreds of billions of dollars.

About 13,800 US soldiers are still in the country, and seven US bases remain to be handed over, according to US military spokesman Major General Jeffrey Buchanan.

Obama's predecessor George W. Bush ordered the invasion of Iraq in 2003, arguing its then leader Saddam Hussein was endangering the world with weapons of mass destruction programmes.

Saddam was toppled, and later executed, but such arms were never found.