Russia issued a stark warning to the U.S. Monday, saying it will treat U.S.-led coalition planes in Syria that fly west of the Euphrates River as targets one day after the U.S. took down a Syrian plane.

The Russian Defense Ministry demanded a full U.S. account as to why it decided to shoot down a Syrian jet Sunday.

Moscow also said it will track all coalition jets and drones west of the Euphrates starting on Monday.

ADVERTISEMENT

Russia is a key ally of Syrian President Bashar Assad in the country’s fight against the Islamic State in Iraq and Syria.

The U.S. military said Syrian Democratic Forces reportedly came under attack from Assad's forces on Sunday afternoon in northern Syria.

The U.S. also said the strike complied with the “rules of engagement and in collective self-defense of Coalition partnered forces.”