General Raymond Thomas, commander of USSOCOM said on Friday that the Russians hold the advantage of possibly expelling US forces from Syria.

He said that because of international law and the fact that the Syrian government under President Assad has not invited the US into his country, the Russians who are Assad’s top ally could eventually force American troops out.

Addressing a security conference at the Aspen Institute, Special Operations Command chief Army General Raymond Thomas said that, while counterterrorism remained a priority for his forces, international law could prevent the U.S. from maintaining a long-term presence in Syria, where its intervention has been declared illegal by the government. Russia is also involved in the fight against the Islamic State militant group (ISIS) and other jihadists in Syria, but entered at the request of Syrian President Bashar al-Assad, something that Thomas said could allow Moscow to make a solid case for the U.S.’s departure.

“Here’s the conundrum: We are operating in the sovereign country of Syria. The Russians, their stalwarts, their backstoppers have already uninvited the Turks from Syria. We’re a bad day away from the Russians saying, ‘Why are you still in Syria, U.S.?,’” Thomas said.

“If the Russians play that card, we could want to stay and have no ability to do it,” he added.

The U.S. and Russia are both battling ISIS in Syria, but they back different factions that hold opposing views on Syria’s political future. The U.S. backs the Syrian Democratic Forces, which Thomas said Special Forces helped name in order to distance themselves from the Kurdish nationalist People’s Protection Units (YPG). Thomas also confirmed that the CIA has cut ties with other Syrian rebel groups that have attempted to overthrow Assad since 2011. Russia and Iran support the Syrian military and its allies, which reject the national aspirations of Kurdish groups, the ultraconservative Sunni Muslim ideology of jihadists and calls for political upheaval by the opposition.

The US and other coalition forces have not been actively targeting Syrian government forces, instead focusing on the fighters of the Islamic State, however, they’ve come under attack from Syrian forces which the US responded.

Syria also conducted a chemical weapons attack on civilians and the US responded by attacking the base where the chemical weapons originated from, something both the Syrians and Russia adamantly deny happened.