Northern Syria (CNN) Kurdish forces guarding a US military base in northern Syria told CNN they feel they've been betrayed by their American allies after US President Donald Trump cleared the way for a Turkish operation against them .

"The Americans sold us out and we do not expect them to help us fight the Turkish troops," one Kurdish fighter told CNN, as a US flag fluttered over the base.

US personnel at the base in northern Syria said they could not speak to CNN due to the sensitive nature of their work here. But, based on comments from the Kurds protecting the base, their relationship has become strained.

Even though US forces have pulled back from the border area where Turkey is staging its military operation to clear Kurdish forces , there are still American military personnel deployed across parts of northern Syria.

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The US still has about 1,000 soldiers in Syria, military officials told CNN and other news outlets. US troops were removed from observation posts within Turkey's operation zone but have not been withdrawn from the country.

Less than an hour after the President made the remark, a senior State Department official reaffirmed the military mission in Syria was ongoing.

"We had and still have a significant military mission there to ensure the enduring defeat of ISIS, also to maintain the stability of northeast Syria and the region given our other critical missions in the near east."

The official expressed serious concerns about the Turkish operation but did not go so far as to criticize Trump.

"It endangers our allies in the fight against terror, the (Syrian Democratic Forces)," the official said. "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."

The SDF have been a key US partner in the fight against ISIS. Shortly after Turkey launched its operation, the SDF suspended their counter-terrorist operations against the group to focus on the Turkish offensive.

For now, US troops are still co-located with SDF elsewhere in Syria and remain in other places such as Manbij, according to a US defense official. While they are still "working" with the SDF, counter-ISIS operations have been suspended so they aren't conducting operations together, according to the same official.

Defense Secretary Mark Esper said Friday the US is not abandoning its Kurdish allies, even as he made clear the US will not intervene in the fight.

"We are not abandoning our Kurdish partner forces and US troops remain with them in other parts of Syria," Esper told reporters at the Pentagon.

"We remain in close coordination with the Syrian Democratic Forces who helped us destroy the physical caliphate of ISIS, but I will not place American service members in the middle of a longstanding conflict between the Turks and the Kurds, this is not why we are in Syria," Esper said.

US advisers have informed the SDF that the US will not defend them from Turkey. And the feeling of abandonment among some Kurds here is palpable.

Outside the American base, a poster commemorates the Kurdish fighters who have died in the battle against ISIS.

On Friday, just a short distance from the base, a funeral was held for a 25-year-old SDF fighter killed by a Turkish mortar round.

A friend of the family, speaking over a loudspeaker, reflected just how raw emotions have become.

"Turkey has been attacking our towns and villages because America gave them permission."