Two US Marines assaulted by Turkish nationalists

(Adds comments by White House secretary paragraph 4)

By Ece Toksabay and Kanishka Singh

ANKARA/WASHINGTON (Reuters) - A nationalist Turkish youth group on Monday attacked two U.S. Marines 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.

White House press secretary Karine Jean-Pierre told reporters on Tuesday that the attack was "a serious matter" and that Washington appreciated the actions of Turkish police.

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" the two dressed in civilian clothes in the Konak district.

It added that five U.S. personnel 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.

The U.S. Embassy to Turkey also confirmed the attack and said the U.S. service members 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 service members on board the ship were Marines and not U.S. Army soldiers, U.S. officials said.

The U.S. Embassy in Ankara had said earlier on Monday that the ship was carrying out a port visit to the Aegean coastal town of Izmir this week.

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 defences that prompted U.S. sanctions and removal from a F-35 jet programme.

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 criticised 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.

(Reporting by Ece Toksabay, Burcu Karakas, Kanishka Singh, Steve Holland and David Ljunggren; Writing by Tuvan Gumrukcu and Kanishka Singh; Editing by Sharon Singleton and Deepa Babington)