Democratic White House candidate Barack Obama was in Iraq on a fact-finding tour on Monday, days after confirming plans to withdraw US troops from Iraq in 16 months if he takes office next year.

He will meet Prime Minister Nuri al-Maliki, President Jalal Talabani and senior US military commanders, Iraqi and US officials said.

"Senator Barack Obama arrived in Iraq this morning as part of a Congressional delegation, along with Senators Jack Reed and Chuck Hagel," embassy spokesman Armand Cucciniello said.

"The senators have a busy day ahead of them, as they meet with senior Iraqi officials, coalition leadership and officials from the US embassy. They will also meet with constituent service members and civilian staff working in Iraq."

It is Obama's second trip to Iraq after a similar Congressional fact-finding tour in January 2006.

He had spent the night in Kuwait after a visit to Kabul, where he pledged to downsize the number of US troops in Iraq and commit at least two more combat brigades to Afghanistan.

Obama's camp has said the aim of his tour is to make an on-the-ground assessment of the war in Iraq and to meet the country's leaders, whom he has criticised for not doing enough to rebuild their country.

"Iraq's leaders have failed to invest tens of billions of dollars in oil revenues in rebuilding their own country, and they have not reached the political accommodation that was the stated purpose of the (US troop) surge," Obama wrote July 14 in The New York Times.

Obama also confirmed his pledge to declare an end to the Iraq war from the first day of his presidency if he wins in November, and to withdraw most US combat troops within 16 months.

Maliki and US President George W. Bush have agreed to include a "time-horizon" for the withdrawal of US forces in a security pact still being negotiated.

The Illinois senator, who voted against the March 2003 war to topple Saddam Hussein, is in Iraq at a time when violence has fallen to a four-year low -- partly on the back of the controversial troop "surge" which he had strongly opposed.

After more than five years at war, with more than 4,100 US troops and tens of thousands of Iraqis killed, Obama said on Sunday it was time to refocus US policy on the region which spawned the September 11 attacks in 2001.

"They have sanctuary here," he said of Al-Qaeda in an interview with CBS in Afghanistan.

"They are gathering huge amounts of money as a consequence of the drug trade in the region. And so, that global network is centred in this area."

Obama called for at least two additional brigades, up to 10,000 troops, to be sent to Afghanistan.

"I think one of the biggest mistakes we've made strategically after 9/11 was to fail to finish the job here, focus our attention here. We got distracted by Iraq," he said.

Republican presidential rival John McCain has lashed out at Obama for announcing his foreign policy even before his fact-finding visits.

"Apparently, he's confident enough that he won't find any facts that might change his opinion or alter his strategy. Remarkable," he said.

German weekly Der Spiegel said Maliki backed Obama's plan to withdraw US troops within 16 months of taking office, but Baghdad has denied the report.

Bush and key ally British Prime Minister Gordon Brown have consistently resisted calls to set a definite timetable for military withdrawals from Iraq.

A poll last Monday underlined why Obama needs to improve his standing on national security issues, and why McCain's team senses he is vulnerable.

Some 72 percent of the 1,119 adults surveyed by telephone in the July 10-13 ABC News/Washington Post poll said McCain, a Vietnam War veteran, would be a good commander in chief. Only 48 percent thought the same of Obama.