US military officials called the publication a security breach that could endanger US troops, and State Department officials said they’d expressed those concerns to Turkish officials.

“We’ve raised our strong concerns with publication of this information with senior Turkish government officials, as we do any time we have concerns about risks to US military or civilian personnel,” one official told BuzzFeed News.

The list, published Tuesday by the Anadolu news agency, detailed not just the location of US bases in Syria, but also provided the approximate number of US troops at each location – information the US has to date refused to divulge. It also provided information about French troops posted alongside them. Turkish officials verified the accuracy of the Anadolu list to The Daily Beast.

The report said Andalou reporters spotted the bases during reporting trips to Syria. The US military said it has not yet determined the source of the information.

US officials privately interpreted the publication as an expression of Turkey’s anger over the US conduct of its war against ISIS, in particular, the US alliance with Kurdish forces that Turkey says are aligned with separatists who’ve been waging a decades-long insurgency against the Turkish state.

The US denies working with the separatists, saying it’s providing support only to the Syrian Democratic Forces, a US-created force that consists of both Kurdish and Arab fighters but that is widely acknowledged to be led by the People’s Protection Units, or YPG, a Syrian Kurdish militia the Turks say is an affiliate of the Kurdistan Workers Party, or the PKK, the Turkish separatist movement. The PKK has been designated a terrorist organization by the US, the European Union, and Turkey.

The Andalou report gave little credence to US assertions about the SDF’s independence. “Despite the fact that the militants were given SDF uniforms, some of them wear uniforms with banners of Abdullah Ocalan, jailed head of PKK terrorist organization in Turkey,” the report said.

The US has deployed more than 1,000 US troops across Syria to advise, train and provide artillery and aerial support to the SDF push to capture Raqqa, ISIS’s Syrian capital. US officials stressed that they already have robust security measures in place, but the US military has cited security precautions previously in declining to release details of the US deployment.

US Central Command, which is responsible for the US operations in the Middle East, made no effort to disguise its dismay that a supposed ally would release those details.

“We are deeply concerned with any information that exposes coalition forces to unnecessary risk being in the public domain,” Centcom spokesman Army Maj. Josh Jacques told BuzzFeed News. “We generally do not disclose the locations of coalition forces operating in Syria to defeat ISIS due to operational security. We remain focused on maintaining the momentum in the continued annihilation of ISIS.”

The publication marks the latest dip in US-Turkey relations that have been troubled for years over US strategy in Syria. Tens of thousands of ISIS fighters used Turkey as a way station in their journey to Syria, amid allegations that the Turkish government was not doing all it could to stanch the flow.

Additionally, Turkish President Recep Tayyip Erdogan has accused the US government of protecting a Pennsylvania-based Turkish cleric, Fethullah Gulen, whom Erdogan blames for last year’s failed coup attempt. Last week, Turkey’s ambassador in Washington told reporters that his government is increasingly frustrated by the slow pace of the US proceedings against Gulen.

“It’s not moving as fast as the Turkish public opinion would like it to move,” Serdar Kılıç said. Meanwhile, the Justice Department has given no indication that it intends to press for Gulen’s extradition to Turkey.

In mid-May, the nations exchanged angry statements over Erdogan’s bodyguards’ beating of demonstrators outside the Turkish ambassador’s residence in Washington. Local prosecutors in Washington eventually charged 12 members of Erdogan’s entourage with crimes in connection with the beatings, which were captured on widely viewed video. Nine people were injured in the melee.

Erdogan was in Washington for meetings with President Donald Trump.