Defense Secretary Mark Esper said Tuesday the United States didn't sign up to fight a war to defend the Kurds against a longstanding NATO ally.

Esper said Turkey should be held accountable for alleged war crimes committed by Turkish-backed proxy forces against the Kurds in Syria.

“I've seen the reports as well, we're trying to monitor them. They are horrible and if accurate and I assume that they are accurate, they would be war crimes,” Esper told CNN. “I think all of those need to be followed up on. I think those responsible should be held accountable, in many cases it would be the government of Turkey -- (it) should be held accountable for this because we cannot allow those things to happen.”