REUTERS/Jason Reed U.S. President Barack Obama checks to see if he still needs the umbrella held by a U.S. Marine to protect him from the rain during a joint news conference with then-Turkish Prime Minister Recep Tayyip Erdogan in the Rose Garden of the White House in Washington, May 16, 2013.

The US and Turkey are headed for a showdown over Syria, as evidence mounts that Ankara is enabling groups that Washington is actively bombing.

Discord between the two allies is now more public than ever following a new report by Dr. Jonathan Schanzer and Merve Tahiroglu of the Foundation for Defense of Democracies.

"Bordering on Terrorism: Turkey’s Syria Policy and the Rise of the Islamic State" details Tu rkey's apparent willingness to allow extremists — including militants from the Islamic State (aka IS, ISIS, or ISIL) — and their enablers to thrive on the 565-mile border with Syria in an attempt to secure the downfall of Syrian dictator Bashar Assad.

"The IS crisis has put Turkey and the US on a collision course," the report says. "Turkey refuses to allow the coalition to launch military strikes from its soil. Its military also merely looked on while IS besieged the Kurdish town of Kobani, just across its border. Turkey negotiated directly with IS in the summer of 2013 to release 49 Turks held by the terrorist group. In return, Ankara reportedly secured the release of 180 IS fighters, many of whom returned to the battlefield.

"Meanwhile, the border continues to serve as a transit point for the illegal sale of oil, the transfer of weapons, and the flow of foreign fighters. Inside Turkey, IS has also established cells for recruiting militants and other logistical operations. All of this has raised questions about Turkey’s value as an American ally, and its place in the NATO alliance."

View photos biden erdogan More

REUTERS/Murad Sezer U.S. Vice President Joe Biden (L) meets with Turkey's President Tayyip Erdogan at Beylerbeyi Palace in Istanbul November 22, 2014.

Schanzer, a former counterterrorism analyst for the US Treasury Department, told Business Insider that Ankara was "like that guy at the casino who keeps doubling down on a bad bet. Each time the policy has failed, Turkey appears to have decided to go back and do it again, but with higher stakes."

Throughout the Syrian civil war, Turkey's southern border has served as a transit point for cheap oil, weapons, foreign fighters, and pillaged antiquities . As the conflict progressed, the fighters taking advantage of Ankara's lax border policies were more and more radical.

"What began with scattered opposition forces exploiting the border became something that was really focused on the Muslim Brotherhood, which then became something that was utilized by [Salafist rebel group] Ahrar al Sham, which was then utilized by [al-Qaeda affiliate] The Nusra Front, which is now utilized by ISIS," Schanzer told Business Insider.

He added that given various reports of jihadi financiers sitting in hotels on the border between Syria and Turkey, "it is impossible that [Turkey's intelligence agency] MIT is not aware" of what's going on.

The financiers "are doling out cash to those who come back with videos of attacks, proof of what they've done against the Assad regime or other enemies," said Schanzer, who previously detailed Turkey's terrorism finance problem to Business Insider. Those videos are then used as propaganda to raise more money for funding fighters.

America's Role

View photos obama More

Story continues