A nationalist Turkish youth group physically assaulted two U.S. soldiers Monday in western Turkey, the U.S. Embassy in Turkey and the local governor's office said, adding that 15 assailants had been detained over the incident.

In a statement, the Izmir governor's office said members of the Turkey Youth Union (TGB), a youth branch of the nationalist opposition Vatan Party, "physically attacked" two U.S. soldiers dressed in civilian clothes in the Konak district.

It added that five U.S. soldiers joined in after seeing the incident, and that police intervened. All 15 attackers had been detained and an investigation was launched into the matter, it said.

A White House spokesperson said Monday, Washington was "troubled" by the assault but added it was "appreciative that Turkish police are taking this matter seriously and holding those responsible accountable."

The U.S. Embassy to Turkey also confirmed the attack and said the U.S. soldiers were now safe.

"We can confirm reports that U.S. service members embarked aboard the USS Wasp were the victims of an assault in Izmir today, and are now safe," it said on social media platform X.

Earlier, the TGB posted a video on X showing a group holding down a man on the street and putting a white hood over his head, while shouting slogans.

The group said the man was a soldier on board the USS Wasp, an amphibious assault ship. The U.S. Embassy in Ankara had said earlier Monday that the ship was carrying out a port visit to the Aegean coastal town of Izmir this week.

"U.S. soldiers who carry the blood of our soldiers and thousands of Palestinians on their hands cannot dirty our country. Every time you step foot in these lands, we will meet you the way you deserve," TGB said.

U.S.-Turkey ties have been strained in recent years by the U.S. alliance with Syrian Kurds that Turkey deems extremists, and over Turkey's purchase of Russian S-400 defenses that prompted U.S. sanctions and removal from a F-35 jet program.

There has also been divergence over Israel's war in Gaza, where over 40,000 people have been killed according to Gaza authorities, and over which Turkish President Tayyip Erdogan has sharply criticized Washington's ally.

Earlier this month, the U.S. ambassador to Turkey said U.S.-Turkey relations are now "in a better place than we've been in a while" and noted the "useful role" Turkey played in a recent prisoner exchange between the United States and Russia.