Congresswoman Liz Cheney tweeted: "Turkey must face serious consequences for mercilessly attacking our Kurdish allies in northern Syria, who incurred thousands of casualties in the fight against ISIS and helped us protect the homeland."

Cheney and nearly thirty of her Republican colleagues in the House will be introducing legislation to impose sanctions against Turkey in response to Ankara’s military offensive against U.S.-allied Kurdish forces in Northern Syria. 

Amid criticism of his decision to pull out of Syria, US President Donald Trump said the United States was “going to possibly do something very, very tough with respect to sanctions and other financial things” against Turkey.

After the US troops moved out of the area following Trump's announcement, Turkish forces moved to northern Syria on Wednesday to launch an assault on the  Kurdish YPG militia which had helped fight the ISIS since 2014.

On the situation, the US official was quoted in media saying "it endangers our allies in the fight against terror, the [Syrian Democratic Forces].”  “It undercuts our efforts to defeat ISIS by drawing these SDF forces away from the battle in the south and frankly forcing our troops to focus on the military aspects of the invasion.”

Critics say the US withdrawal effectively gave Turkey the green light to begin its cross-border assault, which President Recep Tayyip Erdogan says is to create a "safe zone" running for 480km along the Syrian side of the border, BBC reported.

Significantly,  Kurdish militias of the Syrian Democratic Forces (SDF), who were US allies in fight against the Islamic State, control the cross-border areas where the incidents are taking place.

Turkey considers them as 'terrorists'.

The SDF have been key allies of the United States in the battle against the Islamic State (IS) group, and say they have been "stabbed in the back" by the US, reported BBC.

They (SDF) are reportedly still controlling the prisons where the Islamic State captives are lodged, a senior U.S. State Department official said on Thursday, adding that the US has received "a high-level commitment from Turkey on taking responsibility for Islamic State captives but has not yet had detailed discussions, the official said..

It is feared that the Turkish operation can lead to the ethnic cleansing of the Kurds.

It is feared that the move might even revive the ISIS.

Meanwhile, Donald Trump reacted to the development and tweeted: " We defeated 100% of the ISIS Caliphate and no longer have any troops in the area under attack by Turkey, in Syria. We did our job perfectly! Now Turkey is attacking the Kurds, who have been fighting each other for 200 years."

"We have one of three choices: Send in thousands of troops and win Militarily, hit Turkey very hard Financially and with Sanctions, or mediate a deal between Turkey and the Kurds!," he said.

A de-escalation of renewed conflict in northern Syria is “absolutely essential,” the UN Secretary-General António Guterres said on Thursday. His comments follow the launch of airstrikes and a ground offensive by Turkey on Wednesday just days after the United States announced it would pull its troops out of Syria.

Speaking to journalists in Copenhagen, the UN chief said that he did not “believe in military solutions for the Syrian problem, also for any other problem in the world. I always strongly believe in political solutions.”

He also expressed concern over the humanitarian situation and civilian displacement.

The UN Refugee Agency, UNHCR said earlier that tens of thousands of civilians were on the move to escape the fighting.

India's Ministry of External Affairs spokesperson Raveesh Kumar tweeted: "We call upon Turkey to exercise restraint and respect the sovereignty and territorial integrity of Syria. We urge the peaceful settlement of all issues through dialogue and discussion."