James Mattis
© Aaron P. Bernstein / Reuters
The US has "a very active deconfliction line" with Russia in order to not "get drawn into a fight" in Syria, US Secretary of Defense James Mattis said.

Mattis touched upon the ongoing operation in Syria at a press briefing on Tuesday. He said that while the US has coordinated with various "converging forces," it has to maintain high-level interactions with Russia to keep moving against Islamic State (IS, formerly ISIS/ISIL).

"We deconflict with the Russians; it's a very active deconfliction line," Mattis said. "It's on several levels, from the chairman of the Joint Chiefs and the secretary of state with their counterparts in Moscow, General Gerasimov and Minister Lavrov."

"So we just refuse to get drawn into a fight there in the Syria civil war," the secretary of defense said, adding that the conflict can be ended "through diplomatic engagement."

Mattis added that while US forces open fire only on Islamic State enemies, they will fire back "under legitimate self-defense" if somebody "takes a heading on us or fires on us."

On June 18, US-led coalition forces downed a Syrian Su-22 warplane over Raqqa Governorate. Washington justified the attack, saying that the Syrian jet was dropping bombs on US-allied militia fighting ISIS terrorists. Damascus denied the allegations, saying that the plane was carrying out an anti-ISIS operation in the area.

Despite Mattis' statement on the line of communication in Syria, it was not used during that attack. The downing coincided with a Russian warplane mission in the area. Moscow slammed the coalition's actions, calling it "military aggression" against Syria, and demanded an explanation for the downing.

To avoid any such accidents in Syrian airspace, Russia and the US signed the Memorandum on the Prevention of Incidents and Ensuring Air Safety in 2015. The agreement was paused following a US airstrike on Shayrat Airbase on April 7, but the Russian and US militaries kept direct communication channels open. Cooperation was ultimately ended following the coalition's attack on the Syrian military jet.

On Monday, the White House alleged that the Syrian government is preparing "another chemical weapons attack," and threatened retaliation if it occurs. Russia called the threats unacceptable and groundless, recalling that Washington has not provided any hard evidence regarding the April attack in Idlib which provoked the April 7 attack on the airbase, and for which the US still blames Assad.