WASHINGTON — American troops will remain in Syria long after their fight against the Islamic State to ensure that neither Iran nor President Bashar al-Assad of Syria take over areas that have been newly liberated with help from the United States, Secretary of State Rex W. Tillerson said on Wednesday.
Staying in Syria, Mr. Tillerson said, will help ensure that the Trump administration does not repeat what he described as the mistakes of former President Barack Obama, who withdrew troops from Iraq before the extremist threat was doused and failed to stabilize Libya after NATO airstrikes that led to the overthrow of Col. Muammar el-Qaddafi.
“We cannot allow history to repeat itself in Syria,” Mr. Tillerson said during a speech at the Hoover Institution at Stanford University near San Francisco. “ISIS has one foot in the grave, and by maintaining an American military presence in Syria until the full and complete defeat of ISIS is achieved, it will soon have two.”
ISIS is another name for the Islamic State.
There were roughly 2,000 American troops in Syria last month, a mix of engineering units that build fortifications and Special Operations units that fight and train with local militias. Additionally, American military contractors in Syria help demine recaptured areas as the Islamic State is pushed back.
Mr. Tillerson’s comments were the first time a senior Trump administration official pledged to keep American troops in Syria well after the current battle ends. They also marked another step in President Trump’s gradual evolution from a populist firebrand who promised to extricate the United States from foreign military entanglements to one who is grudgingly accepting many of the national security strategies he once derided.
During the presidential campaign, Mr. Trump said that “at some point, we cannot be the policeman of the world.”
Mr. Obama won the White House in 2008 in part by promising to wind down the war in Iraq, and agreed to only a limited role in the 2011 airstrikes in Libya. Mr. Tillerson said those decisions haunt the military officers who now serve in Mr. Trump’s cabinet and, in turn, have led to the administration’s deepening military involvement in Afghanistan.
Mr. Trump has said American forces must remain in Afghanistan because “a hasty withdrawal would create a vacuum for terrorists, including ISIS and Al Qaeda.” Mr. Tillerson repeated that rationale in outlining the administration’s decision to keep forces in Syria.
He did not say whether other countries would help pay for the American military effort or other stabilization costs, even though Mr. Trump also promised during the presidential campaign that he would compel Germany and Persian Gulf nations to contribute financing “because they have the money.”
Mr. Tillerson said the military commitment to Syria was “conditions-based” and not indefinite. But he underscored that it would take time to foster a democratically elected government in Syria that he — like the Obama administration — said would require Mr. Assad’s departure from power.
“Responsible change may not come as immediately as some hope for, but rather through an incremental process of constitutional reform and U.N.-supervised elections,” he said.
Analysts raised concerns that there might never come a time when withdrawal would be deemed appropriate.
“Yes, we can leave troops there for the foreseeable future,” said Gina Abercrombie-Winstanley, a former ambassador and career diplomat. “But is that 20 years, the way Afghanistan soon will be?”
The United States has five key goals in Syria, Mr. Tillerson said. They are: ensuring that the Islamic State and Al Qaeda never re-emerge; supporting the United Nations-led political process; diminishing Iran’s influence; making sure the country is free of weapons of mass destruction; and helping refugees to return after years of civil war.
He conceded the steep challenge in fostering peace and democracy in Syria, where efforts by world leaders and diplomats across the Middle East and the West have fallen short.
Mr. Tillerson is working on a reorganization of the State Department, which so far has resulted in steep budget cuts and the departure of some of its most senior diplomats, including some top Middle East experts. Such expertise is vital to any military or diplomatic ventures in the Middle East, where contradictory and crosscutting rivalries are endemic.
For instance, American backing for a Kurdish-led border force in northeastern Syria has raised alarms in the region and is vehemently opposed by Russia, Turkey, Iran and Mr. Assad’s government. The border force has been described as a “terror army” by President Recep Tayyip Erdogan of Turkey, who worries it will be operated by a Kurdish militia that he considers a threat to his country.
On Wednesday, Deputy Prime Minister Bekir Bozdag of Turkey said his country had reached the limit of its patience regarding developments along its borders.
Mr. Tillerson sought to allay Turkish concerns about the border force.
“Any interim arrangements must be truly representative and must not threaten any neighboring states,” Mr. Tillerson said in the speech.