Speaking at the German Marshall Fund, Esper said Turkey's "unwarranted" invasion into Syria jeopardizes gains made there in recent years as the U.S.-led coalition and allied Syrian Kurdish forces battled the Islamic State group.
"Turkey put us all in a very terrible situation. I think the incursion was unwarranted," he said. "I think President Erdogan was fixated on making this incursion for one reason or another and there was not a possibility that we were going to start a war with a NATO ally."
His comments come on the heels of President Donald Trump's announcement Wednesday that the U.S. is lifting sanctions on Turkey after the NATO ally agreed to permanently stop fighting Kurdish forces in Syria. And he spoke just a day after he was in Iraq to discuss the withdrawal and the Islamic State threat with Iraqi leaders and his military commanders.
Trump has agreed that 200 to 300 U.S. troops will remain at the Al Tanf garrison in southern Syria. And Esper has said the U.S. is still discussing a plan that would leave another small residual force in eastern Syria, near oil facilities that are under the control of the SDF. Those troops would help secure the oil from IS.
Esper is expected to meet with Turkey's defense minister, Hulusi Akar, at the meeting of NATO defense chiefs Thursday. In previous discussions, Esper and other U.S. leaders were unable to convince Turkey to not invade Syria to push back Syrian Kurdish fighters whom Ankara considers terrorists.
Esper's stop in Brussels for the NATO meeting and speech caps a six-day trip that included his first visits as secretary to the two major warzones where U.S. troops are deployed — Iraq and Afghanistan. He also spent several days in Saudi Arabia.
In his speech, Esper also urged allies to join in the effort to help Saudi Arabia defend itself and the broader Gulf region against Iranian threats.
And he repeated familiar warnings about the increasing threats from China and Russia. He said China is trying to reshape the world in its favor, and is using its power to impact other nations' economies and political decisions.
Other nations, he said, must enter their relationships with China with open eyes, and be aware of its militarization of the South China Sea and ongoing thefts of intellectual property.