U.S. Democratic presidential candidate Barack Obama met U.S. military commanders and Iraq's prime minister on Monday to assess security in the country, where there are more than 140,000 American troops.

U.S. strategy in Iraq and troop levels are central issues in the November election race between the first-term senator from Illinois and Republican candidate John McCain.

Obama, who has called for the removal of U.S. combat troops within 16 months of taking office should he win the election, said he had a "very constructive discussion" with Prime Minister Nuri al-Maliki. Television pictures showed the two men smiling and shaking hands before they sat down for talks.

Maliki suggested earlier this month setting a timetable for U.S. troops to leave Iraq, where violence is at a four-year low, but has given no dates.

Obama has welcomed Maliki's suggestion but some Iraqis insist that the army and police cannot go it alone and that a premature withdrawal of U.S. troops could open the door to the sort of violence that nearly tore Iraq apart not so long ago.

On Sunday the Iraqi government denied Maliki told a German magazine in an interview that he backed Obama's plan to withdraw combat troops within 16 months. The government said Maliki's remarks to Der Spiegel were translated incorrectly.

Obama visited Afghanistan over the weekend, the other big foreign policy challenge the next president will face. He called the situation in Afghanistan "precarious and urgent" and said Washington should start planning to transfer more troops there from Iraq.

McCain has attacked Obama for not visiting Iraq recently to get a first-hand look at conditions.

The Republican candidate has been to Iraq eight times while Obama's only other trip was in January 2006, a month before militants blew up a revered Shi'ite shrine in Samarra in an attack that plunged Iraq into vicious sectarian fighting.

The U.S. embassy said Obama, who is visiting Iraq as part of a U.S. congressional delegation, had met the number two U.S. military commander in Iraq and a British general.

He is also expected to hold talks with General David Petraeus, the U.S. commander in the country.

Commanders are likely to tell Obama that security gains are fragile and could be jeopardised by a hasty troop withdrawal.

SECRECY

Obama has scheduled no news conferences in Iraq and his visit has been shrouded in secrecy for security reasons.

Television pictures showed him meeting U.S. troops in the southern city of Basra, the hub for Iraq's oil exports.

Obama, trying to boost his foreign policy credentials, will travel to other countries in the Middle East and visit major powers in Europe this week.

But he courted controversy on July 3 when he said he might "refine" his views on withdrawing combat troops from Iraq within 16 months but later said his stance had been unchanged for more than a year and that he intended "to end this war".

McCain says the U.S. troop buildup last year helped boost stability in Iraq and has criticised the Democrat's vow to order a quick withdrawal as "reckless".

But the dramatic reduction in violence has led Baghdad to become increasingly assertive about its own security capabilities.

Indeed, Maliki and President George W. Bush agreed last week to set a "time horizon" for reducing American forces in Iraq.

It was the closest the Bush administration has come to acknowledging the need for a timeframe for U.S. troop cuts. Bush has long opposed deadlines for troop withdrawals.

In a speech last Tuesday, Obama said a "single-minded" focus on Iraq was distracting the United States from other threats.

Bush ordered 30,000 extra troops to Iraq in early 2007 to try to drag the country back from the brink of all-out war between majority Shi'ites and minority Sunni Arabs.

The last of those reinforcements depart this week, still leaving 140,000 U.S. soldiers in the country, about the same number as when Bush ordered the so-called surge.