Russia denounced the downing of a Syrian Air Force warplane by a Navy fighter jet as an act of “military aggression” on Monday and threatened to target aircraft belonging to the US-led coalition in the war-torn Middle East country.

“Any aircraft, including the international coalition’s planes and drones, discovered west of the river Euphrates, will be accompanied by ground and air-based anti-aircraft defenses as aerial targets,” Russia’s defense ministry said in a statement on Monday.

The US said it acted in “collective self-defense” when a F-18 Super Hornet on Sunday shot down a Syrian SU-22 that had attacked a site near Tabqa occupied by members of the Syrian Democratic Forces.

The Syrian militia is assisting the US-led coalition in its efforts to wipe out Islamic State terrorists.

It was the first time the US military shot down a Syrian warplane in the six years of civil war in the country.

Syria said its plane was targeting militants with the terror group.

White House spokesman Sean Spicer said the US would continue to protect its interests in the region.

“The escalation of hostilities doesn’t help anybody and the Syrian regime and others in the regime need to understand that we will keep the right to self defense,” he said.

Increasing tensions in the area, Iran on Sunday fired missiles at ISIS targets in Syria in retaliation for attacks that killed 18 in Tehran last week. ISIS claimed responsibility for the killings.

Iran vowed to respond militarily to further attacks and included the US in the warning.

“This attack, before being a message for the terrorists, is a message for the supporters of terrorism in the region which are symbolized by the Saudi regime and the Americans,” Iranian lawmaker Javad Karimi Qoddousi said on Monday, according to Iranian state television’s website.

Russia, which is propping up the regime of President Bashar al-Assad, said the downing violated international law and went against a safety agreement between the two countries to lessen the risk of incidents involving their aircraft in Syria.

“Multiple military actions of U.S. aviation under the guise of fighting terrorism against the legal military of a state that is a member of the United Nations are a flagrant violation of international law and constitute de facto military aggression against the Syrian Arab Republic,” the ministry said. “We view these actions by the American command as a conscious failure to uphold their responsibilities within the memorandum.”

The Kremlin temporarily suspended the 2015 agreement in April after the US struck a Syrian airbase with Tomahawk missiles in retaliation for a chemical attack Assad ordered on his people.

A spokesman for the American-led coalition Operation Inherent Resolve said the US would continue flights.

“We are going to continue to conduct operations throughout Syria, providing air support for coalition and partnered forces on the ground,” Col. Ryan Dillon told the New York Times.

Franz Klintsevich, a top Kremlin lawmaker, blamed President Trump and said the “naked aggression” was aimed at Russia.

“It looks like Donald Trump’s United States is a source of a brand-new danger both in the Middle East and the world at large,” Klintsevich wrote on Facebook.

Russian deputy foreign minister Sergei Ryabkov said the attack actually aided the terror group.

“This, if you like, is help for the terrorists that the US are fighting under what they call their anti-terrorism policy,” Ryabkov said.

With Wires