In a decision bound to infuriate Turkey, a senior Trump administration official said that heavier weapons would be approved for Syrian Kurdish forces as they close in on the Islamic State capital of Raqqa.

The anonymous senior official was quoted by the Associated Press as part of its coverage of Defense Secretary James Mattis’ meetings on Syria. NBC News published similar quotes by two unnamed defense officials, who said the Kurds could receive rifles, ammunition, armor, communications gear, and engineering equipment, delivered by ground convoys and air drops. NBC’s sources did not go into detail about what type of heavy weapons might be sent to the Kurds.

Military Times reported over the weekend that elite YPG fighters are already armed with advanced American combat gear, including night-vision goggles, digital camouflage, body armor, and the type of rifles used by American special operations forces. Photos of YPG commandos with American gear began appearing online during the battle to capture the strategic town of Tabqa, west of Raqqa, in late March.

U.S. military officials have only acknowledged supplying the YPG with Russian-made weapons, such as the ubiquitous AK-47 rifle. Officials “offered only ambiguous responses” when asked how the Kurdish fighters acquired American gear. Military Times anticipated Turkey would be “infuriated.”

Dana White, chief spokeswoman for the Defense Department, issued a statement on Tuesday formally acknowledging President Trump’s decision:

Yesterday, the president authorized the Department of Defense to equip Kurdish elements of the Syrian Democratic Forces as necessary to ensure a clear victory over ISIS in Raqqa, Syria.

The SDF, partnered with enabling support from U.S. and coalition forces, are the only force on the ground that can successfully seize Raqqa in the near future.

We are keenly aware of the security concerns of our coalition partner Turkey. We want to reassure the people and government of Turkey that the U.S. is committed to preventing additional security risks and protecting our NATO ally.

The U.S. continues to prioritize our support for Arab elements of the SDF. Raqqa and all liberated territory should return to the governance of local Syrian Arabs.

The fight for Raqqa will be long and difficult, but will ultimately be yet another defeat for ISIS, and another step toward eliminating the ISIS threat to peace and security in the region and the world.

Turkey’s response will largely depend on whether they acknowledge a significant difference between the Kurdish YPG militia and the Syrian Democratic Forces (SDF), an umbrella group of Arabs, Assyrians, and other groups led by the Kurds against ISIS, al-Qaeda, and the Syrian regime.

American analysts have expressed a high degree of confidence in the training, discipline, and fighting ability of the SDF. The U.S. military has such a good relationship with the SDF that some American soldiers participated in an SDF ceremony recently at which some 250 female veterans of the YPG militia were inducted into Syrian Democratic Forces ranks.

The U.S. Central Command reportedly sent Mattis a request last week asking to arm the Kurds. Defense officials and analysts said Mattis and President Trump were likely to approve the plan, which envisioned a mixed Kurdish and Arab force supported by American artillery and airstrikes to push ISIS out of Raqqa. The Obama administration also believed Kurdish troops would be key to recapturing the city, but President Barack Obama was said to be reluctant to approve the plan for Raqqa so close to Trump taking office.

Reuters described Mattis as “upbeat” after meeting with a Turkish official in Copenhagen, Denmark on Tuesday. Mattis said the administration intended to “work with the Turks, alongside one another, to take Raqqa down, and we’re going to sort it out and we’ll figure out how we’re going to do it.”

However, U.S. officials said Mattis was not signaling a new agreement with Turkey about the battle plan for Raqqa, and maintained the Trump administration is skeptical of Turkey’s claims that it can manage the liberation of Raqqa without Kurdish help.

Turkey adamantly insists that the Syrian Kurdish YPG militia is allied with the banned Kurdistan Workers Party (PKK) in Turkey, a Kurdish separatist organization that both Turkey and the United States classify as terrorist in nature. On the other hand, the U.S. views the YPG as an invaluable battlefield ally against the Islamic State, and quietly rejects Turkish characterizations of the Syrian Kurdish militia as an offshoot of the PKK.

Turkey has not merely been critical of the YPG – it has attacked Kurdish positions in Syria, prompting military responses from the Kurds. One of Turkey’s professed strategic goals in Syria is preventing the Kurds from annexing all or part of Raqqa. Kurdish leaders have said that if the people of Raqqa wish to join their autonomous “democratic federal” system after the Islamic State is defeated, that would be fine with them.

The U.S. military has been patrolling the Turkey-Syria border to discourage further Turkish attacks on the Kurds. Turkish officials have suggested they might not care if American troops get in the way during their next operation against the YPG.

Mattis also said that he was reviewing the Russian proposal to create “safe zones” for refugees in Syria, a proposal co-sponsored by Turkey and Iran.

“It’s all in process right now,” Mattis said en route to Copenhagen Monday. “Who is going to be ensuring they’re safe? Who is signing up for it? Who is specifically to be kept out of them? All these details are to be worked out and we’re engaged.”

Mattis said another important consideration was whether the safe zone proposal would affect the battle against the Islamic State – a distinct possibility, since the safe zones are supposed to be no-fly zones for all military aircraft, including those belonging to the United States and its anti-ISIS coalition partners.

Turkish President Recep Tayyip Erdogan is scheduled to meet with President Donald Trump on May 16. Erdogan has already suggested the American alliance with Syrian Kurds would be the top item on the agenda.