President Donald Trump has threatened to "devastate" Turkey economically if the NATO-allied nation attacks US-backed Kurdish forces in Syria following a pullout of American troops from the war-torn country, in a stern warning rejected by Ankara saying it will continue to fight the "terrorists".

The US troop withdrawal has left America's Kurdish allies vulnerable to an attack from Turkey. Ankara views the Kurdish forces as terrorists aligned with insurgents inside Turkey.

"Starting the long overdue pullout from Syria while hitting the little remaining ISIS territorial caliphate hard, and from many directions. Will attack again from existing nearby base if it reforms," the president said in a tweet on Sunday.

"Will devastate Turkey economically if they hit Kurds. Create 20-mile safe zone.... Likewise, do not want the Kurds to provoke Turkey," Trump said in a hard-hitting tweet on Sunday.

Trump's tweet is a stark threat toward an ally in the region that has partnered with the US in the fight against ISIS.

In a sharp response, Turkish President Recep Tayyip Erdogan's spokesman Ibrahim Kalin said that there was "no difference" between the Islamic State extremist group and the Kurdish People's Protection Units (YPG) militia.

"Mr Donald Trump, Terrorists can't be your partners & allies. Turkey expects the US to honour our strategic partnership and doesn't want it to be shadowed by terrorist propaganda. There is no difference between DAESH, PKK, PYD and YPG. We will continue to fight against them all," Kalin said in a tweet.

"Mr Donald Trump It is a fatal mistake to equate Syrian Kurds with the PKK, which is on the US terrorists list, and its Syria branch PYD/YPG. Turkey fights against terrorists, not Kurds. We will protect Kurds and other Syrians against all terrorist threats," he said.

Trump also warned ISIS that America would hit them hard from nearby military bases if it regains momentum.

Last week, Turkish President Erdogan hit out at US National Security Adviser John Bolton for saying the US withdrawal was contingent upon Turkey's pledge not to attack US-backed Kurdish fighters in Syria once troops leave.

"Bolton made a serious mistake. If he thinks that way, he is in a big mistake. We will not compromise," Erdogan said.

The Pentagon has said that there is no timeline for US troop withdrawal and it would be based on ground realties.

"Russia, Iran and Syria have been the biggest beneficiaries of the long-term US 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!" Trump said.

His announcement has come following a visit to the region by Bolton and Secretary of State Mike Pompeo.

"The roughly 2,000 uniformed soldiers that are in Syria today are going to be withdrawn. That activity is underway. We're going to do so in an orderly, deliberate way, a way that protects America's national security, a way that allows us to continue the important mission that they were on," Pompeo told CBS News in an interview on Sunday.

"The counterterrorism mission, the effort to make sure that the destruction of ISIS is not only complete but that their resurgence is not possible, our efforts to counter the threat from terrorism stemming from the Islamic Republic of Iran those are all real missions. The tactical change we've made in the withdrawal of those 2,000 troops is just that, a tactical change," he said.

Noting that the mission remains the same, Pompeo said Turkish leadership has made it clear that it understands there are people down in Syria that have their rights.

"We also want to make sure that those in Syria aren't attacking, terrorists aren't attacking Turkey from Syria. We're fully engaged," he said, responding to a question if Turkey has promised the US not to attack the Kurdish allies.

Pompeo argued that there was no danger to American interest even after its withdrawal from Syria.

"The United States of America can project military power from lots of places in the world. The absence of a couple thousand soldiers on the ground in Syria in no way materially diminishes the capacity of the United States of America and our amazing Armed Forces to deliver American power to accomplish our objectives anywhere in the world," he said.

"That certainly includes in Syria. It certainly includes into Iran, if need be. We still have those tools. American diplomats still have that leverage and that power standing behind them. I am very confident in our military capabilities here in the Middle East," Pompeo said.

Ground troops first arrived in Syria in autumn 2015 when then-President Barack Obama sent in a small number of special forces to train and advise YPG fighters.

A peaceful uprising against the president of Syria President Bashar al-Assad seven years ago turned into a full-scale civil war. The conflict has left more than 350,000 people dead, devastated cities and drawn in other countries.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)