Kurdish fighters said Sunday that Syrian government troops will help them fend off Turkey's invasion at the northern border, The Associated Press reported.

The decision to ally with Syrian President Bashar Assad came after President Trump ordered the withdrawal of U.S. troops from the northeastern part of the country, drawing backlash from Democrats and Republicans alike.

Turkish President Recep Tayyip Erdoğan launched an operation against Syrian Kurds last week shortly after the announcement of the withdrawal of U.S. forces.

The U.S. had more than 1,000 troops deployed in the region to work with the Kurdish YPG, which leads the Syrian Democratic Forces in the fight against the Islamic State in Iraq and Syria (ISIS).

The U.S. has valued the Kurdish group as a vital collaborator to defeat ISIS.

The YPG is a top enemy for Ankara, however, which sees it as an offshoot of the Kurdistan Workers' Party (PKK), a Kurdish separatist movement based in Turkey. Both the U.S. and Turkey consider the PKK a terrorist organization.

Trump has defended his decision to withdraw U.S. troops from Syria, saying he wants to remove the U.S. from "endless wars."

Defense Secretary Mark Esper on Sunday said the withdrawal is needed because of the increasing danger posed by the fighting between Turkey and the Kurds.

"We have American forces likely caught between two opposing advancing armies, and it's a very untenable situation," he said on CBS's "Face the Nation."