Trump landed at 7:16 pm local time at Al-Asad Air Base in western Iraq, accompanied by his wife Melania Trump, an AFP correspondent said. The president spoke to troops and met with military leaders before leaving a few hours later.

Although the visit took place in considerable secrecy, speculation had been mounting that Trump might make such a trip following his controversial decision to slash troop levels in Afghanistan and pull out entirely from Syria.

"President Trump and the First Lady traveled to Iraq late on Christmas night to visit with our troops and Senior Military leadership to thank them for their service, their success, and their sacrifice and to wish them a Merry Christmas," White House spokeswoman Sarah Sanders tweeted.

Melania Trump's spokeswoman called it "a surprise visit to our brave U.S. service members currently deployed in Iraq."

Presidential trips to boost troop morale have been a longstanding tradition in the years of war following the September 11, 2001 terrorist attacks, and Trump has taken considerable criticism for declining to make such a visit until now.

But apart from the photo ops alongside uniformed military members, Trump was expected to use the Iraq trip to further explain his decision to end the Syria deployment and cut troop levels in Afghanistan.

- Time to pull troops? -

The policy changes, defended by Trump as an exit from wars where the United States no longer needs to be expending lives and money, have sparked alarm among US allies and some in the US security establishment.

The drawdowns -- and the abrupt way that they were announced -- helped lead to the resignation of Trump's defense secretary, Jim Mattis, who has been one of the administration's key heavyweights.

In his unusually forcefully worded resignation letter, Mattis appeared to chide Trump when he stressed his own "strongly held" views on "treating allies with respect and also being clear-eyed about both malign actors and strategic competitors."

Trump also took flak from France and other allies and senior figures in his own Republican party.

However, the president has made disentangling America from seemingly endless wars a priority since his 2016 election and he says the time is right.

The Islamic State jihadist group, which once controlled swaths of territory in Iraq and Syria, has been driven mostly into hiding, allowing the approximately 2,000 US troops supporting local fighters to leave soon, Trump says.

And in Afghanistan, he wants to withdraw about half of the 14,000 soldiers locked in a war against Taliban guerrillas that has long resembled a stalemate.

"Does the USA want to be the Policeman of the Middle East, getting NOTHING but spending precious lives and trillions of dollars protecting others who, in almost all cases, do not appreciate what we are doing?" Trump asked in a tweet recently.

"Do we want to be there forever? Time for others to finally fight," he tweeted.