Amid a sharp escalation of tensions among the various parties drawn into Syria’s civil war, the Pentagon’s top military officer tried to defuse a clash with Russia a day after the U.S. military shot down a Syrian fighter jet attacking coalition forces engaged in the battle to defeat the Islamic State group.

Gen. Joseph F. Dunford, chairman of the Joint Chiefs of Staff, said the U.S. and Russian military had been in contact after Moscow angrily announced that it was shutting down a hotline designed to avoid unintentional clashes between American and Russian fighters operating in the skies above Syria and would even target U.S. and allied planes if they strayed from their zone.

“That link is still ongoing here this morning,” Gen. Dunford said at a National Press Club talk in Washington.

He said the administration will “work diplomatically and militarily in the coming hours to re-establish deconfliction” with Russian forces in Syria.

The downing of a Syrian-flagged SU-22 fighter on Sunday, coupled with recent hostilities by pro-regime Iranian paramilitaries against U.S. bases along the Syrian-Iraqi border, has sharpened the Syrian conflict to a level not seen since the beginning of the war against the Islamic State three years ago.

Analysts say the exchanges also are a sign of the maneuvering by the major players in the Syrian crisis to lay down markers and stake claims ahead of what most expect to be the imminent collapse of the Islamic State’s “caliphate,” centered in the city of Raqqa.

Russia’s rhetoric was unusually harsh in the wake of the downing of a plane of its ally, Syrian President Bashar Assad. Deputy Foreign Minister Sergei Ryabkov on Monday called it “another act of defiance of international law by the United States.”

Russian warplanes and military advisers have been backing Mr. Assad against Western-backed rebel groups in the country’s brutal 6-year-old civil war.

“Regardless of who is in power in Washington they are in the habit of thinking that there are certain circumstances that enable them to take high-handed, contemptuous attitudes and in some cases to openly ignore the ABCs of international conduct,” Mr. Ryabkov said.

A statement from the Pentagon said the downing of the Syrian jet was “in accordance with rules of engagement and in collective self-defense of coalition-partnered forces.”

When asked if U.S. aircraft were in danger of being shot down by Russian or Syrian warplanes, Gen. Dunford replied: “I’m confident that we are still communicating between our operations center and the Russian Federation operations center. And I’m also confident that our forces have the capability to take care of themselves.”

Breaking point

Russia’s decision Monday marked the second time it has suspended communications designed to avoid unintended clashes with the U.S. and its allies in Syria’s fractured battlefield. Communications were temporarily cut in April when President Trump ordered a series of Tomahawk cruise missile strikes in response to Damascus’ suspected use of chemical weapons against anti-government forces.

The line was re-established weeks later, but military relations between Washington and Moscow in Syria eroded significantly in the wake of the cruise missile strikes. The Trump administration maintained that the April strikes were not a sign of Washington’s desire to take a side in the Syrian civil war.

White House spokesman Sean Spicer sounded a similar tone on Monday. He said the Islamic State, not the Assad regime and its Russian allies, “represents a threat to all nations.”

Despite Moscow’s saber-rattling, the U.S. intends to keep “the lines of communication open with the Russians to deconflict potential issues,” Mr. Spicer said during a press briefing.

But he added that the U.S. will do whatever is necessary to protect America’s military and its interests in Syria. “Obviously, we’re going to do what we can to protect our interests,” he said. “We will always preserve the right of self-defense.”

American commanders said they were acting in self-defense when they took out the Syrian fighter near the town of Ja’Din, located south of Tabqa dam, the coalition’s main logistics and air support hub for the assault on Raqqa.

Pro-Assad forces launched an attack on Ja’Din on Sunday afternoon and retook the town from the Syrian Democratic Forces, the network of Arab and Kurdish militias allied with the U.S. coalition in the Raqqa fight.

It was unclear whether the regime forces that led the assault on Ja’Din were government troops or Iranian paramilitaries sent in by Tehran to support the regime.

After the assault on Ja’Din, the Syrian SU-22 fighter launched airstrikes on SDF fighters taking back their positions inside the city. Coalition commanders ordered a Navy F/A-18 Super Hornet to intercept and destroy the enemy aircraft.

“We made every effort to warn [pro-regime forces] not to come any closer. And then the commander made a judgment that there was a threat to the forces that we were supporting, and took action,” Gen. Dunford said Monday.

He said it was the second time U.S. warplanes have taken out regime targets threatening coalition forces.

American fighters took out a column of Iranian paramilitary forces allied with the Assad regime this month after they attempted to cross into a secure perimeter around a U.S. training camp in the southern Syrian city of At Tanf. Russian and Syrian leaders have agreed not to enter the area surrounding the camp.

Shortly after the U.S. airstrikes, a foreign drone reportedly bombed a joint U.S. and Syrian patrol outside the At Tanf camp. Coalition officials confirmed there were no casualties from the attack but declined to comment on whether Iran had launched the drone.

Beyond Raqqa

The U.S. special operations camp at At Tanf was one of the coalition’s main training hubs for moderate Syrian militias — including elements of the Free Syrian Army — spearheading coalition operations against Islamic State fighters in Deir el-Zour and the Eastern Euphrates River Valley.

Top Islamic State leaders, including “caliph” Abu Bakr al-Baghdadi, reportedly began fleeing Raqqa for Deir el-Zour and Madan en masse in May, ahead of the coalition’s operation to liberate the city starting this month.

Deir el-Zour and the surrounding river valley is expected to be the battleground against the Islamic State once Raqqa falls.

Emboldened by the regime’s victory over anti-government forces in the rebel stronghold of Aleppo late last year, military commanders in Damascus, Tehran and Moscow are increasingly setting their sights on Deir el-Zour. Since March, the Assad regime has carried out offensives against in Deir Hafer, an Islamic State enclave 30 miles east of Aleppo, and al Bab. Government troops seized al Bab in February and took control of the main roadways leading from the city into Raqqa.

That presence, seen as an attempt by Mr. Assad to maintain sway over the country and gain leverage during ongoing peace talks, has posed problems for American and coalition commanders trying to maintain order among the various forces battling the Islamic State in northern Syria.

Looking to leverage that momentum by regime forces, Iranian militias have taken a more aggressive posture. Aside from amassing Shiite militiamen around the U.S. base at Al Tanf, Tehran launched a series of ballistic missile strikes against Islamic State targets in and around Deir el-Zour.

The ballistic missile strikes, the first ever taken by Iran against the Islamic State, were in retaliation for a series of terrorist attacks in Tehran claimed by the jihadi group. The Tehran strikes in June, which left 18 dead and 40 wounded, were the first actions the Islamic State took inside the Iranian capital.

The missile strikes hit the “headquarters and gathering centers of Takfiri terrorists supporting and building car bombs,” said a statement by the hard-line Islamic Revolutionary Guard Corps broadcast Sunday by Tasnim news.