A group of about 20 nationalists attacked three U.S. sailors in Istanbul on Wednesday, hurling objects at them, chasing them and briefly putting a bag over one of the sailors’ heads.

The U.S. Navy acknowledged the incident, which was publicized in a video online. The attack underscores the volatility in Turkey, a longtime U.S. ally that increasingly is at odds with Washington on foreign policy, especially over how to handle the Islamic State militant group in neighboring Syria.

In the video, one of the Turks is seen saying the Americans looked like members of the U.S. Army. The Turks claimed to be members of the Turkey Youth Union, which is opposed to working with the United States and becoming members of the European Union.

“We define you as murderers, as killers… and we want you to get out of our land,” one man says, seconds before the attack ensues.

The Navy said the sailors were assigned to the USS Ross, a destroyer, and in Turkey for a scheduled port visit. They appeared to be in their late teens or early 20s. They were able to get away without suffering injuries and are back on the Ross, Navy officials said.

“The U.S. Navy is currently working with the Turkish National Police and U.S. Embassy staff to investigate this incident,” said a statement from U.S. Naval Forces Europe/Africa. “The U.S. Navy will continue to coordinate with Turkish authorities to review security procedures for future ship visits.”

In a series of tweets, the U.S. Embassy in Turkey blasted the attack, calling it appalling. The vast majority of Turks are against “an action that so disrespects Turkey’s reputation for hospitality.”

A Navy spokesman, Lt. Timothy Hawkins, said that the Ross already was scheduled to depart Istanbul on Thursday and that the attack had no effect on operations.

Navy Secretary Ray Mabus said in a Facebook post that he is certain the vast majority of Turkish people and the Ankara government do not condone the attack.

“We understand that local law enforcement have suspects in custody,” Mabus said. “We commend this swift action and are certain that those who did this will be held accountable.”