A defense official in Washington said some military cargo has been pulled out, part of what the military calls the start of a "deliberate withdrawal" from Syria, where about 2,000 troops have been working with a coalition of Syrian Kurdish and Arab fighters to defeat the remnants of the Islamic State group.
The U.S. involvement in the war-torn country has shifted from working quietly behind the scenes to support rebels to overt displays of U.S. force and a gradually widening footprint in an attempt to shape the fight.
The following is a timeline of the U.S.'s involvement in Syria's conflict that erupted in March 2011.
March 2011: Protests erupt in the southern Syrian city of Daraa over security forces' detention of a group of boys accused of painting anti-government graffiti on the walls of their school. Demonstrations spread, as does the crackdown by President Bashar Assad's forces.
August 2011: President Barack Obama calls on Assad to resign and orders Syrian government assets frozen.
June 2013: U.S. officials conclude that Assad's forces had used chemical weapons against the opposition. Obama authorizes direct support for the rebels.
Aug. 20, 2012: Obama famously describes the use by Assad's government of chemical weapons a "red line" that would draw U.S. retaliation.
Aug. 21, 2013: Hundreds of people suffocate in rebel-held suburbs of the Syrian capital. U.N. investigators visit the sites and determine that ground-to-ground missiles loaded with sarin were fired on civilian areas while residents slept. The U.S. and others blame the Syrian government.
Aug. 31, 2013: Obama says he will go to Congress for authorization to carry out punitive strikes against the Syrian government, but appears to lack the necessary support in the legislature. He is widely criticized for not committing to his "red line" comment.
Summer of 2014: The U.S. administration reveals that several dozen special operations troops had been on the ground in Syria briefly in an effort to rescue foreign hostages taken by the Islamic State group, but did not find them.
Sept. 22, 2014: Obama launches a U.S. air campaign against the Islamic State in Syria, one month after launching airstrikes in neighboring Iraq. To date, the U.S.-led coalition has launched airstrikes on at least 17,000 locations in Syria since the start of the operation.
Late 2015: The first American ground troops enter Syria — initially 50, growing to the current official total of about 2,000. They recruit, organize and advise thousands of Syrian Kurdish and Arab fighters, dubbed the Syrian Democratic Forces, and push IS out of most of its strongholds.
November 24, 2016: Senior Chief Petty Officer Scott Cooper Dayton, 42, of Woodbridge, Virginia, is killed in an improvised explosive device blast near the northern Syrian town of Ayn Issa, becoming the first American casualty in combat in the fight against IS in Syria.
April 4, 2017: More than 90 people are killed in a suspected nerve gas attack on the town of Khan Sheikhoun in the rebel-held Idlib province. Moscow and Damascus deny responsibility.
April 5, 2017: Trump says Assad's government has "crossed a lot of lines" with the suspected chemical attack in Syria and a day later, the U.S. fires 59 cruise missiles into Syria in retaliation — the first direct American assault on the Syrian government.
March 30, 2018: U.S. Master Sgt. Jonathan J. Dunbar is killed by a roadside bomb attack in Syria alongside a British serviceman.
April 7, 2018: Syrian activists, rescuers and medics say a poison gas attack on the rebel-held town of Douma near the capital has killed at least 40 people. The Syrian government and Russia reject the allegations, saying the purported evidence of the chemical weapons attack was fabricated.
April 8, 2018: Trump calls Assad an "animal" and says there would be a "big price to pay" for resorting to outlawed weapons of mass destruction.
April 15, 2018: The United State, Britain and France launch missile attacks on the Syrian capital Damascus and the central province of Homs in retaliation for the Douma attack. Syria says its air defenses intercepted most of the missiles fired.
December 19, 2018: Trump announces on Twitter his intention to withdraw troops from Syria, adding in a video posted to Twitter, "now it's time for our troops to come back home." The withdrawal is initially expected to be carried out within weeks.
Dec. 21, 2018: Defense Secretary Jim Mattis and Brett McGurk, the administration's special envoy to the global anti-IS coalition, resign in protest.
Jan. 6, 2019: U.S. national security adviser John Bolton says during a visit to Israel that U.S. troops will not leave northeastern Syria until IS militants are defeated and American-allied Kurdish fighters are protected. The comments appear to put the brakes on the withdrawal abruptly announced by Trump.
Jan. 8, 2019: Turkish President Recep Tayyip Erdogan accuses the U.S. national security adviser of making "a very serious mistake" by demanding that Ankara guarantee the safety of Kurdish fighters in northeastern Syria before the U.S. withdraws its troops.
Jan. 11, 2019: A U.S. defense official in Washington says some military cargo has been pulled out of Syria, marking the beginning of the withdrawal process.