Turkish jets bomb U.S.-backed Kurdish fighters in Syria, Iraq

April 25 (UPI) -- Turkish military jets carried out strikes against U.S.-backed Kurdish fighters in northern Iraq and northeast Syria, killing at least 70 people, according to a Turkish military statement.

Turkey's air force said in a statement the strikes Tuesday were against against the Kurdistan Workers' Party in the Sinjar Mountains region in northern Iraq, which is close to the Syrian border and in the Karachok Mountains in northeastern Syria.

"This is very serious," an unidentified U.S. official told Fox News.

About an hour before 24 Turkish jets and two Turkish drones bombed the areas, Turkey warned U.S. and Russian troops near the planned attack. Russian officials' pleas not to strike were ignored, U.S. officials said.

No American troops were among the fighters who were hit, the officials said.

About 1,000 U.S. troops are on the ground in Syria. In March, 400 Marines were sent to Syria to support U.S.-backed troops fighting around Raqqa.

The United States considers the Popular Protection Units, known as the YPG, as key allies against Islamic State.

But Turkey said it sought to prevent the Kurdistan Workers' Party, PKK, from sending "terrorists, arms, ammunition and explosives to Turkey," the statement said, and it was conducted "within the scope of the international law."

Turkish warplanes targeted the headquarters of the General Command of the YPG in Mount Karachok, as well as the media center, a local radio station, communication headquarters and some military institution.

The Syrian Observatory for Human Rights said that at least 18 YPG fighters were killed in the Syrian strikes.

Separately, strikes killed at least six fighters from the Peshmerga, the military forces of the autonomous region of Iraqi Kurdistan. The Peshmerga, which has friendly relations with Turkey, said the attack was "unacceptable" and called on PKK forces to withdraw.