Australia has suspended all air operations over Syria in the wake of US forces downing a Syrian jet and a warning from Russia that US-led coalition planes are now targets for its forces in parts of the country.
It's the latest twist in a conflict that one analyst has described as undergoing a "dramatic escalation" as an "uneasy battlefield coexistence" between forces with competing aims proves impossible to maintain.
In a statement, the Australian Department of Defence -- part of the international coalition fighting ISIS in the country -- said: "As a precautionary measure, Australian Defence Force (ADF) strike operations into Syria have temporarily ceased.
"ADF force protection is regularly reviewed in response to a range of potential threats. ADF personnel are closely monitoring the air situation in Syria and a decision on the resumption of ADF air operations in Syria will be made in due course. ADF operations in Iraq will continue as part of the coalition."
Russian threat
The news comes after a US Navy fighter jet shot down a Syrian warplane on Sunday. The US said it shot down the plane to defend the US-backed Syrian Democratic Forces (SDF), a rebel group which is fighting ISIS on the outskirts of Raqqa, the ISIS stronghold in northeast Syria.
The incident -- the first of its kind since the US started fighting ISIS in Syria in 2014 -- prompted Russia to issue a threat to coalition aircraft flying west of the River Euphrates.
The Russian Ministry of Defense called the downing of the plane "a cynical violation of the sovereignty of the Syrian Arab Republic" and "military aggression."
As a result, it said, Russia has stopped using a key "de-confliction" communication channel set up to avoid conflict between US and Russian forces in Syria.
The Russian Defense Ministry said in a statement: "From now on, in areas where Russian aviation performs combat missions in the skies of Syria, any airborne objects found west of the Euphrates River, including aircraft and unmanned vehicles belonging to the international coalition, tracked by means of Russian land and air anti-aircraft defense, will be considered air targets."
Dramatic escalation
Gayle Tzemach Lemmon, a senior fellow at the Council on Foreign Relations, said Monday that the downing of the Syrian jet, together with Iran firing missiles into Syria over the weekend, marked "a dramatic escalation in a war the United States had not intended to fight".
Lemmon said: "These events illustrate how an uneasy battlefield coexistence in Syria has spiraled into a situation that is impossible to maintain."
Forces with competing aims are currently at close quarters in eastern Syria.
The United States is aggressively backing the SDF, a Syrian rebel alliance, as it fights its way into Raqqa, supported by intense coalition airstrikes.
Meanwhile the Syrian army and its allies are also closing in on Raqqa and last week the Syrian military reached areas controlled by the SDF, making clashes between the opposing alliances almost inevitable.
When the Syrian air force bombed SDF positions Sunday, the US came to the aid of its partners on the ground -- and the Syrian jet was downed.
Meanwhile Iran's military said Sunday that it has launched several medium range ballistic missiles into eastern Syria, targeting ISIS fighters in retaliation for twin attacks that rocked Tehran on June 7.
The strikes are the first time Iran has fired missiles at another country in three decades and represent a major escalation of Iran's role in the war in Syria.