US-led coalition strikes pro-Assad forces in Syria
The US-led coalition fighting the Islamic State group in Syria has struck pro-government forces, the Pentagon confirmed.
It said the attack occurred after forces supporting Syrian president Bashar Assad entered an area near a coalition base in southern Syria with a tank, artillery, anti-aircraft weapons, other vehicles and more than 60 soldiers.
A statement said the pro-Assad forces ignored several coalition warnings.
The Pentagon statement did not further identify the targeted forces.
But in recent weeks, officials have complained about various militants refusing to leave an area near Tanf, Syria.
The US and its partners train Syrian rebels there to fight IS.
The coalition struck similarly described forces in the area last month.
Earlier, a US-backed Syrian force began an offensive to capture the northern city of Raqqa, the de facto capital of IS, after months of clearing operations.
An American commander said the battle will be long and difficult, but success would deliver a "decisive blow" to the extremists.
By early afternoon on Tuesday, opposition activists said the Kurdish-led Syrian Democratic Forces (SDF) were trying to break into the city from the east, triggering intense clashes.
Raqqa was among the first cities captured by IS in January 2014, and has been the home of some of the group's most prominent leaders.
Talal Sillo, a spokesman for the SDF, confirmed operations had begun in co-ordination with the US-led coalition.
"We declare today the beginning of the great battle to liberate the city of Raqqa, the alleged capital of terrorism and terrorists," he said.
"Morale is high and military readiness to implement the military plan is complete."
SDF fighters began advancing towards Raqqa in November, capturing wide areas of northern Syria from the extremists. Last week, they reached the northern and eastern gates of the city after intense clashes under the cover of US-led air strikes.
Raqqa is currently surrounded from the east, north and west, and opposition activists have reported intense shelling and air strikes on the city since Monday night, which killed at least 12 people.
IS militants are not expected to give up easily. Iraqi forces launched an offensive to capture the northern city of Mosul, the largest in that country held by IS, in October and heavy fighting continues there.
Lt Gen Steve Townsend, the top US commander in Iraq, said the twin offensives against Mosul and Raqqa are harming Islamic State's prestige and ability to recruit new loyalists.
"It's hard to convince new recruits that IS is a winning cause when they just lost their twin 'capitals' in both Iraq and Syria," he said.
He added that US-led coalition forces will continue to support the SDF in Raqqa, providing equipment, training, intelligence and logistics as well as precision firepower.
"We all saw the heinous attack in Manchester, England," said Mr Townsend, referring to the bombing that killed 22 people last month and was claimed by IS.
"IS threatens all of our nations, not just Iraq and Syria, but in our own homelands as well. This cannot stand.
"The international coalition and our partner forces are steadily dismantling the physical caliphate of IS.
"Once IS is defeated in both Mosul and Raqqa, there will still be a lot of hard fighting ahead, but this coalition is strong and committed to the complete annihilation of IS in both Iraq and Syria."
Mr Townsend added that once Raqqa is retaken, the SDF have stated it will be turned over to a representative body of local civilians who will provide security and governance.