Speaking to Al Monitor, Jeffrey said: “Erdogan will not back down until you show him teeth. That’s what we did when we negotiated the cease-fire in October of 2019. We were ready to crush the economy.”

The U.S. threatened to impose sanctions on Turkey unless it ended an assault on Kurdish-led forces in north-eastern Syria at the end of last year. Turkey eventually halted its advance, giving rise to an uneasy stand-off across the region.

The Turkish military operation came after U.S. President Trump ordered U.S. troops to withdraw from north-eastern Syria, a decision Jeffrey said followed conversations with Erdogan.

Turkey accuses the Kurdish-led Syrian Democratic Forces (SDF) of links to the outlawed Kurdistan Workers’ Party (PKK), with which it has been engaged in an internal conflict since the 1980s.

“Trump was uncomfortable about those (Kurdish-led) forces, and he trusted Erdogan”, Jeffrey said.

Critics sympatric to the SDF have accused Jeffrey of paving the way for the Turkish assault on the group, which resulted in allegations of war crimes including ethnic cleaning. But Jeffrey said he was seeking to reach a viable compromise to avoid conflict.

“The Kurds were always trying to get us to pretend that we would defend them against the Turkish army… There was no plan to respond to the Turks because (the U.S. military) had no order to do that. That was not part of their mission set,” he said.

“The US military had no authorization to shoot at the Turks, who could simply drive around them.”

However, Jeffrey said reaching an accommodation with Turkey was central to U.S. interests in combating Russia and Iran.

“The NATO radar that is the core of the entire anti-ballistic missile system defending against Iran is in Turkey. We have tremendous military assets there. We really can’t ‘do’ the Middle East, the Caucuses or the Black Sea without Turkey. And Turkey is a natural opponent of Russia and Iran.”

Reporter's code: 50101