US shoots down Syrian fighter jet that attacked coalition forces, Pentagon says

At least 117 killed in US-backed Syrian offensive to expel Islamic State

About two hours later, a Syrian jet dropped bombs and was "immediately" shot down by a US war plane, the coalition said.

The US-led coalition headquarters in Iraq said in a written statement that a USF-18 Super Hornet shot down a Syrian government SU-22 after it dropped bombs near the US partner forces, known as the Syrian Democratic Forces.

Following the downing of the Syrian plane, clashes between government troops and coalition-backed fighters broke out in two villages some 40km south of the city of Raqqa, the Syrian Observatory for Human Rights said.

Meanwhile, the Syrian army warned of the "dangerous repercussions" of the attack, stressing that such acts will not dissuade the Syrian army from carrying on with fighting the terrorist groups and restoring peace and security to all of Syria.

The coalition confirmed that a U.S. Navy F/A-18E Super Hornet shot down a Syrian Su-22 that had dropped bombs near SDF positions. The pilot is missing, The Syrian Armed Forces said.

USA -backed forces have encircled the city of Raqqa and captured several districts from the militants.

Tanf is a key town on the Iraq-Syrian border that has been home to a U.S. Special Operations training outpost for months.

Coalition aircraft in a show of force stopped the initial advance.

The Combined Joint Task Force stressed that the coalition's mission is to defeat IS.

The coalition does "not seek to fight the Syrian regime, Russian or pro-regime forces" but would not "hesitate to defend itself or its "partnered forces from any threat", the statement said".

Russian Federation said on Saturday that airstrikes carried out this month had killed about 180 Islamic State (IS) jihadists in Syria, including two field commanders.

- Editor's note: This story will be updated.