Syrian fighters backed by US special forces battled Thursday to clear the last remaining Islamic State (IS) militant group holed up in their crumbling stronghold of Raqa.
Across the border in Iraq, security forces were attacking all remaining territory held by the extremists, who are fighting to prevent the all-out collapse of their self-proclaimed "caliphate".
Most of Raqa, long a byword for IS most gruesome atrocities, is now in the hands of US-backed fighters supported by waves of heavy air strikes by a military coalition led by Washington.
"The Syrian Democratic Forces and American special forces began a mopping up operation in Raqa," the Syrian Observatory for Human Rights said Thursday.
The Britain-based monitor said IS holdouts were still hiding in underground shelters in a part of the city centre where a football stadium and former government buildings are located.
But the operation was being slowed down by large numbers of mines planted by IS in the city, where they have been under siege for three months, it said.
The extremists seized Raqa in early 2014, making it their de facto Syria capital. They are thought to have used the city to plan attacks abroad.
On Wednesday the SDF said they were in the "final stages" of capturing Raqa as the Observatory said the US-backed fighters controlled 90 percent of the northern city.
The US-led coalition supporting the SDF estimated that 65-70 percent of Raqa was under the control of the alliance of Kurdish and Arab fighters.
Across the border In Iraq, security forces backed by paramilitary units launched a dawn assault on a besieged IS-held pocket around the northern town of Hawija, just days after attacking IS only other foothold in the country.
The territory still held by IS has been dwindling fast since its defeat in Iraq s second city Mosul in July, with stronghold after stronghold coming under assault on both sides of the border with Syria.
Iraqi Prime Minister Haider al-Abadi predicted the assault on the Hawija region would swiftly bring a new victory against the crumbling IS.
After the defeat of IS in Mosul and the recapture of adjacent areas, Hawija and neighbouring towns form the last enclave still held by IS in Iraq apart from a section of the Euphrates Valley downstream from the border with Syria.
"Greetings to all of our forces, who are waging several battles of liberation at the same time and who are winning victory after victory and this will be another, with the help of God," Abadi said.
An AFP correspondent heard heavy shelling around the IS-held town of Sharqat where Iraqi forces have been massing in recent days.
The US-led coalition fighting IS hailed the new offensive by the Iraqi security forces against IS, also known as ISIS.
"Daesh is losing ground and failing in every battle. Soon ISIS will have no sanctuary in Iraq," said coalition spokesman Colonel Ryan Dillon.
Humanitarian organisations expressed concern for the fate of civilians caught up in the offensive.
"The 85,000 civilians still in and around Hawija, including around 40,000 children, now face a terrifying time as they worry about getting caught up in the fighting or being hit by an air strike," said International Rescue Committee acting country director Jason Kajer.
"For those who decide to flee, there is a significant risk of being targeted by ISIS snipers or killed by a mine."
In Syria, tens of thousands of civilians have fled the Raqa fighting in recent months but thousands are still trapped inside the city according to the UN S Office for the Coordination of Humanitarian Affairs (OCHA).
"We now estimate that up to 15,000 civilians remain trapped in Raqa city, although exact figures remain difficult to verify due to the situation on the ground," OCHA s Linda Tom told AFP.
She said the civilians, many of them women and children, "are facing incredibly difficult conditions", including food, water and medical shortages.
IS has seen the territory under its control fast diminish in recent months in the face of multiple offensives against its fighters in both Iraq and Syria.
On Tuesday, Iraqi forces launched an attack up the Euphrates Valley against the other one of IS s two remaining enclaves in Iraq.
And in Syria s eastern province of Deir Ezzor, IS faces twin assaults -- one by Russian-backed government troops and the other by SDF fighters.
IS also holds pockets of territory elsewhere in Syria, notably in eastern parts of the central provinces of Homs and Hama, but it has come under attack by Russian-backed government forces there too.
