BEIRUT, Reuters, Jun 19, 2017 – The United States and Iran have flexed their military muscles in unprecedented ways in Syria to deter attacks on their allies and interests, with Russia warning Washington on Monday it would treat any U.S.-led coalition planes in its area of operations as potential targets after the U.S. military downed a Syrian jet.

Tensions escalated on Sunday as the U.S. military brought down the jet near Raqqa for bombing near U.S.-allied forces on the ground, and Iran launched missiles at Islamic State targets in eastern Syria – the first time each state has carried out such actions in the multi-sided Syrian war.

While aimed at Islamic State, the Iranian strike was also a projection of military power into part of Syria identified as a top priority by Damascus and its allies, and followed a recent tussle with Washington over a section of the Syria-Iraq border.

The tensions reflect mounting competition for areas of Syria where Islamic State (IS) insurgents are in retreat, leaving swathes of territory up for grabs and posing the question of what comes next for U.S. policy that is shaped first and foremost by the priority of vanquishing the jihadists.

The United States said the Syrian army plane shot down on Sunday had dropped bombs near fighters of the Syrian Democratic Forces (SDF), a U.S.-backed alliance of Kurdish and Arab fighters battling to capture the city of Raqqa from IS.

Russia’s Defence Ministry responded on Monday by suspending cooperation with the United States aimed at avoiding air incidents over Syria, where the Russian air force is bombing in support of Assad’s campaigns against rebels and IS.

The Syrian army said the jet was shot down while flying a mission against Islamic State.

The SDF however accused the Syrian government on Monday of attacking its positions using planes, artillery and tanks. “If the regime continues attacking our positions in Raqqa province, we will be forced to retaliate,” SDF spokesman Talal Silo said.

The Syrian government this month marched into Raqqa province from the west but had avoided conflict with the U.S.-backed SDF until the latest incident.

“The SDF is getting big-headed,” said the pro-Damascus military commander, a non-Syrian who spoke to Reuters on condition of anonymity. “There could be problems between it and Soheil Hassan,” said the commander, referring to the Syrian officer leading the government offensive in Raqqa province.

Yezid Sayigh, a senior fellow at the Carnegie Middle East Center in Beirut, said the sides were establishing red lines in a fluid situation, and the Syrian government was “always testing and pushing the boundaries”

“I don’t think the Americans are testing the red lines. They are saying ‘we have a red line here and if you are going to test it we will respond, but it doesn’t mean we are now shifting strategy’ because they also want to reassure the Russians.”

The United States has said its recent actions against Syrian government forces and allied militia have been self-defensive in nature, aimed at stopping attacks on U.S.-led coalition forces or their local allies.

These have included several air strikes against pro-government forces that have sought to advance towards a U.S. base in southeastern Syria near the border with Iraq, where the U.S. military has been training Syrian rebels to fight IS.

The area is of strategic significance to Tehran as it seeks to secure a land corridor to its allies in Iraq, Syria and Lebanon and establish a “Shi’ite crescent” of influence that has long concerned U.S.-allied states in the Middle East.