The United States will not allow NATO member Turkey to attack U.S.-allied Kurds in Syria, Secretary of Defense Mark Esper declared this week.

Syrian Kurds helped the U.S.-led coalition dismantle the so-called Islamic State (ISIS/ISIL) territorial caliphate that once spawned across swathes of Iraq and Syria.

The Pentagon chief told reporters on Tuesday that “unilateral action” against the Syrian Kurds by Turkey “would be unacceptable.”

“What we’re trying to do now is work out with them an arrangement to address their concerns, and I’m hopeful we’ll get there,” he added.

Esper further noted that the United States is “trying to convince Turkey not to invade” Syria and push the Kurds out.

The Pentagon chief stressed that the United States would not “abandon” the northern Syrian Kurds considered terrorists by Turkey.

While speaking to reporters on Tuesday, the Pentagon chief added:

We don’t have any ambition to abandon them [Syrian Kurds], if you will. But at the same time, what we’re going to do is prevent unilateral incursions [by Turkey ] that would upset, again, these mutual interests that both the United States, Turkey and the SDF [Syrian Democratic Forces] share with regard to Syria.

The anti-ISIS SDF is a U.S.-backed Kurdish-Arab alliance led and dominated by the People’s Protection Units (YPG), the armed wing of the Democratic Union Party (PYD).

With the help of the United States, PYG officials maintain control of large swathes of northern Syria along the Turkish border

On Sunday, Turkish President Recep Tayyip Erdogan revealed that he has shared with Russia and the United States his plan to carry out an offensive against the Kurds’ region of Syria.

Erdogan has long been pushing for an attack on the People’s Protection Units (YPG) in Syria despite U.S. warnings against the move.

A Turkish attack on the Kurds would threaten the fragile stability created by the complete fall of the ISIS caliphate in March, the U.S. official argued.

Esper indicated that the United States has no immediate plan in place to end its support of the SDF.

Echoing some U.S. officials, Turkey has long linked the YPG of being to the Kurdistan Worker’s Party (PKK). Militants from the PKK have been waging a decades-long insurgency on Turkish soil.

The U.S., Turkey, and other NATO members have deemed the PKK to be a terrorist group.

The political wing SDF denied any links to the PKK. Secretary Esper spoke to reporters about the Turkish threat against the Syrian Kurds while en route to Tokyo.

Asked whether the United States has abandoned the Syrian Kurds post, Esper responded:

We don’t have any ambition to abandon them, if you will. But at the same time, what we’re going to do is prevent unilateral incursions that would upset, again, these mutual interests that both the United States, Turkey and the SDF share with regard to Syria.

The U.S. secretary of defense acknowledged that the United States keeps in touch with the SDF, telling reporters: “We continue to talk with the SDF in the region. I’m not going to convey any more than that at this time. But we stay in contact with them, as much as we do with the Turks.”

The Pentagon chief reiterated that the United States is “heavily engaged with the Turks with regard to their security interests in northern Syria.”

According to U.S. government and independent assessments, ISIS remains a threat in Syria post-the demise of its territorial caliphate.

On Tuesday, the Pentagon’s inspector general (IG) released a report warning about the ongoing menace the jihadi group, particularly “ISIS sleeper cells,” represent.

The new IG report noted that a “partial withdrawal” of U.S. troops from Syria “decreased” the ability of local forces “to respond to ISIS resurgent cells.”

The report, which covers added:

The Iraqi Security Forces (ISF) and U.S.-backed Syrian Democratic Forces (SDF) were unable to sustain long-term operations against ISIS militants. It said that in Iraq, the ISF often lacks the ability to maintain hold forces in territory cleared of ISIS militants, while in Syria, the SDF was “initially limited” in personnel, equipment, and intelligence to confront ISIS’s resurgent cells.

…

[The U.S.-led coalition] also reported that ISIS has established “resurgent cells” in areas controlled by Syrian partner forces. While Syrian forces carried out clearance operations in northeastern Syria to eliminate these cells, [the U.S.-led coalition] reported that U.S.-backed Syrian forces also have limited capacity to hold liberated areas.

Even after the fall of the caliphate, the U.S.-backed Iraqi forces and SDF continue to struggle to contain ISIS.

“ISIS likely retains between 14,000 and 18,000 ‘members’ in Iraq and Syria, including up to 3,000 foreigners,” the Pentagon IG found.

Al-Qaeda-linked jihadis have also gained control of most of Idlib and the territory around it, marking the last remaining rebel stronghold.