BAGHDAD (Reuters) - The United States counts on its regular communications with Russia to help avoid a conflict with Iranian-backed forces threatening U.S. and U.S.-backed forces in southern Syria, a U.S. envoy in Baghdad said on Wednesday.
Brett McGurk, the American envoy to the international coalition against Islamic State, said a U.S. air strike on Tuesday against Iranian-backed fighters in Syria supporting Syrian President Bashar al-Assad was meant to defend American forces there.
A military alliance fighting in support of President Bashar al-Assad said on Wednesday it could hit U.S. positions in Syria, warning that its "self-restraint" over U.S. air strikes on government forces would end if Washington crossed "red lines".
The U.S. military, which has sought to stay out of Syria's civil war and instead focus its firepower on Islamic State militants in Syria and Iraq, has repeatedly warned pro-Assad forces to stay away from a so-called "de-confliction" zone near their garrison near the southern Syrian town of At Tanf.
McGurk said it speaks daily with the Russian military to avoid misunderstandings with pro-Assad forces, which Moscow backs, but the zone had recently been shelled and the U.S. forces there had to defend themselves.
"We really do depend upon the Russians through our de-confliction military channels ... to help work these things out, and so we hope obviously that will not happen again," he said, referring to the strikes on the Iranian-backed forces.
The U.S. military launched a similar air strike on Iranian-backed forces in Syria on May 18.
The warning from the self-described "commander of the operations room of the forces allied to Syria" was circulated by a military news unit run by the Lebanese group Hezbollah, one of Assad's military allies.
"America knows well that the blood of the sons of Syria, the Syrian Arab Army, and its allies is not cheap, and the capacity to strike their positions in Syria, and their surroundings, is available when circumstances will it," the statement said.
A Syrian military source said Tuesday's strike had caused deaths and material damage and showed the coalition was "in support of terrorism". The Syrian military command warned against the dangers of escalation, the source added.
McGurk said the U.S.-backed campaign to capture Raqqa, Islamic State's de-facto capital in Syria, would accelerate "but this will be a long term effort".
"They are down to their last neighborhood in Mosul and they already lost part of Raqqa, and the Raqqa campaign from here will only accelerate," he said.
The U.S.-backed, Kurdish-led Syrian Democratic Forces said on Tuesday it had launched an operation to capture Raqqa, in an assault that overlaps with the final stages of the U.S.-backed attack to recapture the Iraqi city of Mosul.
U.S.-backed rebels took At Tanf from Islamic State last year and regional intelligence sources say they mean to use it as a launchpad to capture Bukamal, a town on Syria's border with Iraq and an important jihadist supply route.
The coalition's presence in Tanf, on the Damascus-Baghdad highway, was also meant to stop Iran-backed groups from opening an overland route between Iraq and Syria, the sources say.
Writing by Maher Chmaytelli; Editing by Tom Heneghan