Turkey's military is set to cross into northern Syria "shortly," the Turkish communications director said, as part of an impending offensive to move US-backed Kurdish forces away from its border.

“Turkish military, together with the Free Syrian Army, will cross the Turkish-Syrian border shortly,” Fahrettin Altun, the Turkish government communications director tweeted from a verified account in the early hours of Wednesday morning from Istanbul.

Altun added that the Kurdish People's Protection Units, also known as the YPG, had two options: “They can defect or we will have stop them from disrupting our counter-ISIS efforts.”

The expected offensive comes days after US President Donald Trump provoked a storm of criticism, including within his own party, by announcing that US troops would be pulled back from the border area.

Trump's decision effectively provides Turkish troops with a green light to attack US-backed Kurdish forces, though Trump threatened to punish Turkey economically if it does “anything outside of what we think is humane.”

Ankara regards the YPG as a terrorist group affiliated with the Kurdistan Workers’ Party (PKK), which has fought the Turkish state for more than three decades. But the US backs the YPG and credits the Kurds for helping defeat ISIS in Syria.

The Kurdish-led Syrian Democratic Forces (SDF) said Tuesday that “all indications” point to a Turkish attack on its border areas and called on the international community to help avoid a possible humanitarian disaster.

In a series of tweets from the verified Twitter account of the SDF, the General Command said the border areas of northeast Syria “are on the edge of a possible humanitarian catastrophe. All indications, field information and military assembly on the Turkish side of the border indicate that our border areas will be attacked by Turkey.”

“This attack will spill the blood of thousands of innocent civilians because our border areas are overcrowded,” the SDF said. It went on to call on the international community and those countries fighting against ISIS “to carry out their responsibilities” to avoid a “possible impending humanitarian disaster.”

Separately, the group claimed Tuesday that the Turkish military shelled one of its points in northeastern Syria on the border with Turkey in an “unprovoked attack.”

The SDF, which has vowed to defend itself against any perceived Turkish incursion, called on the US-led coalition and the international community to implement a no-fly zone over northern Syria similar to the one implemented in Iraq.

The Turkish Defense Ministry said Tuesday that the Turkish Armed Forces is “the only coalition and NATO army fighting the DAESH (ISIS) terrorist group in the Euphrates Shield Operation.”

“Turkey is one of the countries most affected by DAESH's bloody activities and has fought against this terrorist organization both domestically and beyond its borders with increasing tempo and intensity,” the ministry said in a tweet posted on its official twitter page.

The Euphrates Shield Operation, launched in July 2014 inside Syrian territory, was not only aimed at fighting ISIS but also the YPG.

On Saturday, Turkish President Recep Tayyip Erdogan announced that the country had “completed our preparations and action plan” and was ready to launch a “ground and air operation” east of the Euphrates river, with the goal of establishing “peace” by clearing the region of “terrorists.”

Reinforcements deployed by the Turkish army could be seen arriving at the border town of Akcakale on Tuesday, according to the state-owned Anadolu news agency.

Turkey won't ‘bow to threats’

The Kurds have long been considered as among Washington's most reliable partners in Syria and in the broader campaign against ISIS in the region.

US-backed Kurdish forces have been responsible for holding all captured ISIS fighters in the area. However, according to the White House, this responsibility will now fall to Turkey.

Trump has defended his decision to remove US troops from the area, saying he was “not siding with anybody” — Kurdish forces or the Turkish government — and reiterated an earlier warning to Turkey about potential economic devastation.

“I told Turkey if they do anything outside of what we think is humane … they could suffer the wrath of an extremely decimated economy,” the President said.

Turkish Vice President Fuat Oktay said his country won't “bow to threats” in an apparent response to Trump's warning.

“Turkey will teach a lesson to terror organizations that threatens our southern border and we will give an opportunity for Syrian refugees who are currently in Turkey,” Oktay said. “Our message to international community is clear. Turkey is not a country that will bow to threats.”

The abrupt move, announced in a Sunday night statement from the White House press secretary following a call between Trump and Erdogan, has prompted a rare show of bipartisan opposition to the Republican President.

Trump has faced a barrage of criticism from within his own party, including Senate Majority Leader Mitch McConnell, Sen. Lindsey Graham and former US Ambassador to the UN Nikki Haley about the decision.

And the former top American general overseeing operations in the Middle East said Trump's “decision to seemingly abandon our Kurdish partners could not come at a worse time.”

“The decision was made without consulting US allies or senior US military leadership and threatens to affect future partnerships at precisely the time we need them most,” retired Gen. Joseph Votel, who led US Central Command from March 2016 to March 2019, wrote in an opinion piece in The Atlantic.