Turkish President Recep Tayyip Erdogan last month invited President Donald Trump to visit Turkey in 2019 | Brendan Smialowski/AFP via Getty Images Trump threatens Turkey with economic devastation There have been concerns Turks might attack Kurdish forces once American troops are gone.

U.S. President Donald Trump on Sunday vowed to “devastate Turkey economically” should the Turkish military attack U.S.-allied Kurdish fighters — a rare direct threat by Trump to a NATO ally as his administration grapples with the execution of its plan to withdraw American soldiers from Syria.

“Starting the long overdue pullout from Syria while hitting the little remaining ISIS territorial caliphate hard, and from many directions,” Trump tweeted. “Will attack again from existing nearby base if it reforms. Will devastate Turkey economically if they hit Kurds. Create 20 mile safe zone....”

The president also wrote online: “....Likewise, do not want the Kurds to provoke Turkey. Russia, Iran and Syria have been the biggest beneficiaries of the long term U.S. policy of destroying ISIS in Syria - natural enemies. We also benefit but it is now time to bring our troops back home. Stop the ENDLESS WARS!”

The planned U.S. troop drawdown has provoked international uncertainty amid conflicting statements from senior administration officials deployed in recent days to help calm regional powers.

Turkey has supported American efforts against ISIS. But the Turks consider Kurds, who are also fighting ISIS, to be their enemy, and there have been concerns they might attack the Kurdish forces once the American troops are gone.

National Security Adviser John Bolton appeared to contradict the president in Jerusalem last weekend when he said the Syria withdrawal is conditioned on defeating the remnants of the Islamic State and on Turkey assuring the safety of the Kurds. Those remarks were met with indignation from Turkish President Recep Tayyip Erdoğan.

Secretary of State Mike Pompeo, currently on an eight-day tour of the Middle East, described Trump’s Syria policy on Saturday as “incredibly clear.” He characterized the withdrawal as merely “a tactical change” in U.S. military strategy and said the “mission remains the same” in regard to the administration’s efforts to destroy the Islamic State group and terror threats from Iran.

In a phone conversation Saturday, Pompeo and Turkish Foreign Minister Mevlüt Çavuşoğlu “agreed on the importance of continuing U.S.-Turkish consultations,” according to a State Department spokesman.

Erdoğan last month invited Trump to visit Turkey in 2019, the White House confirmed, and White House spokesman Hogan Gidley said the president “is open to a potential meeting in the future.”