He will meet Prime Minister Nouri al-Maliki, President Jalal Talabani and senior U.S. military commanders, Iraqi and U.S. 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 U.S. 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 U.S. 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 criticized 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 [U.S. troop] surge," Obama wrote on 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 U.S. combat troops within 16 months.

Residents of Baghdad's Sadr City, the stronghold of anti-American Shiite cleric Moqtada al-Sadr, were skeptical of Obama's plans.

"This proclamation is a mere political stunt," said Abu Ali, 43. "The American policy would not change with the change in the president, especially the military policy which is planned by far sighted commanders."

But Sunni Arab Khalaf Marhoon from Haweeja in the northern oil province of Kirkuk said he felt that if Obama became the next president it would change "the face of the Iraq war."

"I feel confident about Obama when he makes announcements of withdrawing the U.S. military from Iraq," he told AFP.

Maliki and U.S. 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 U.S. troops and tens of thousands of Iraqis killed, Obama said on Sunday it was time to refocus U.S. policy on the region which spawned the Sept. 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 centered 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 U.S. 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.

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

OBAMA PLAN FOR IRAQ

Iraq remains one of the top issues in the U.S. presidential campaign, five years after the U.S.-led invasion toppled late dictator Saddam Hussein and plunged the United States into a bloody conflict.

Democratic White House hopeful Barack Obama said as far back as 2002 that the war was a bad idea, but he was not in the Senate when the fateful vote was taken to authorize the invasion.

TROOPS

The Illinois senator has pledged to immediately start bringing home U.S. combat troops from Iraq if elected, at the rate of one or two combat brigades a month until all combat troops are home within 16 months.

In a major speech on Iraq this week, he pledged the wrest the "single-minded" U.S. focus away from the country, and to pour at least two more combat brigades into Afghanistan amid worsening security.

"Iraq is not going to be a perfect place, and we don't have unlimited resources to try to make it one," Obama said in the speech in Washington.

"I will give our military a new mission on my first day in office: ending this war," Obama said.

He said however he would listen to generals and make tactical adjustments to his plan where necessary, and bring pull troops out of least volatile areas first.

PERMANENT BASES

Obama is opposed to establishing permanent bases in Iraq, but says he would keep some troops in the country to protect U.S. embassies and diplomatic buildings, and to conduct anti-terror missions.

IRAQI GOVERNMENT

Obama says he will press Iraqi leaders to achieve reconciliation and take over responsibility for running the country, envisaging that the United Nations will have a central role to play in this.

"What I will not do is to continue to let the Iraqi government off the hook and allow them to put our foreign policy on ice, while they dither about making decisions about how they're going to cooperate with each other," he said in April.

REGIONAL STABILITY

The Democratic senator plans to involve all Iraq's neighbors, including international pariahs Iran and Syria, in a new approach for regional stability to secure Iraq's borders, stop outside meddling in its politics and support reconstruction.

"Because if [Iraqi Prime Minister Nouri al-Maliki] can tolerate normal neighbor-to-neighbor relations in Iran, then we should be talking to them as well," Obama told the Senate in April.

"I do not believe we're going to be able to stabilize the situation without them."

REFUGEES

Obama plans to set up an international working group to address the issue of refugees, with some two million displaced within Iraq. He will also provide $2 billion to support refugees outside Iraq.

JUSTICE

"Iraqis must know that those who engage in mass violence will be brought to justice. We should lead in forming a commission at the U.N. to monitor and hold accountable perpetrators of war crimes within Iraq," Obama said in September.