American officials are sounding the alarm over a possible large-scale military operation by Turkey in northern Syria, targeting US-backed Kurdish-controlled areas.

According to the same sources, significant Turkish military forces, consisting of militias, special forces and heavy artillery, have massed on the border near Kobani, a Kurdish-majority town.

The gathering of forces began after the deposition of the Assad regime in early December, strongly reminiscent of Ankara’s moves before its 2019 invasion of northeastern Syria. “We are monitoring the situation and pushing for restraint,” a U.S. official said.

According to the Wall Street Journal, Ilham Ahmed, a Kurdish civil administration official, sent a letter to US President-elect Donald Trump asking him to intervene and persuade Turkish President Recep Tayyip Erdogan not to proceed with another invasion. “Turkey’s goal is to impose its control over our territories before you take office, forcing you to engage with them as masters of our territory,” Ahmed said in his letter, warning of “disastrous consequences” in the event of Turkish intervention.

The development has put the Kurdish-led Syrian Democratic Forces (SDF) in a vulnerable position. Foreign Secretary Anthony Blinken traveled to Turkey last week to discuss Syria’s future with Erdogan and seek assurances that Ankara would limit operations against Kurdish militants.

However, US-brokered ceasefire talks between Syrian Kurds and Turkey-backed rebels in Kobani collapsed on Monday without agreement, according to a spokesman for the Syrian Democratic Forces. The SDF are now observing “significant military concentrations” east and west of the city, the spokesman said.

“From the border, we can already see Turkish forces massing and civilians living in constant fear of imminent death and destruction,” Ahmed wrote to Trump.

Ahmed warned that a Turkish attack would displace more than 200,000 Kurdish civilians in Kobani and recalled Trump’s pledge in an earlier meeting that the United States “will not abandon the Kurds.”

Ahmed urged President-elect Trump to use his influence to prevent a Turkish invasion and protect Kurdish communities that have been staunch allies in the battle for peace and security. “Erdogan, he has heard your voice in the past,” he said, “and we believe your leadership can prevent this catastrophe.”