Hundreds of people fled the Fallujah area Friday as forces pressed simultaneous offensives on the Iraqi city and on another of the Islamic State group's key bastions in Syria.

An estimated 50,000 civilians remained trapped in Fallujah city however as well as twice that number along Syria's border with Turkey as a result of an IS sweep near Aleppo.

The US-led coalition claimed it killed a key IS commander for the Fallujah area, although it was not clear when.

"We've killed more than 70 enemy fighters, including Maher Al-Bilawi, who is the commander of ISIL (IS) forces in Fallujah," coalition spokesman Steve Warren said.

Warren said the IS commander was killed two days ago while an Iraqi officer and a local official had reported his death last week.

Tens of thousands of Iraqi forces on May 22-23 launched an offensive to retake Fallujah, one of only two major Iraqi cities still controlled by IS, the other being Mosul.

IS fighters holed up in Fallujah are believed to number around 1,000 and while the myriad forces involved in the operation have moved closer, none have yet entered the city proper.

Fallujah is one of IS's most important bastions.

It was the first Iraqi city to fall out of government control in January 2014 and was the scene a decade earlier of some of the worst fighting US forces had seen since the Vietnam war.

The city has been surrounded by pro-government forces for months and concern has been mounting among humanitarian groups that the population was being deliberately starved.

- Trapped civilians -

"The situation inside Fallujah is getting critical by the day," said Nasr Muflahi, the Norwegian Refugee Council's Iraq director.

Despite plans before the operation for safe corridors, few civilians have managed to flee the Fallujah battle in recent days.

The biggest group slipped out on Friday.

"Our forces evacuated 460 people... most of them women and children," said police Lieutenant General Raed Shakir Jawdat.

IS "gave us food that only animals would eat," Umm Omar, who was accompanied by more than 10 members of her family, said.

Across the border, IS's de-facto Syrian capital Raqa was also coming under increasing pressure.

A Kurdish-Arab alliance has launched an operation to retake the city, where an estimated 300,000 people still living there are becoming increasingly desperate to flee.

According to anti-IS activist group Raqa is Being Slaughtered Silently (RBSS), residents were paying smugglers $400 (350 euros) each to try to escape.

"There is nearly no one walking in the streets," said RBSS activist Hamoud al-Musa.

"People are afraid of a brutal onslaught from the warplanes, whether coalition, Russian, or even regime," he told AFP.

IS had set up a few new checkpoints in Raqa city and was "amassing its forces on the front lines" further north, he said.

- 'Disaster' near Turkish border -

Along Syria's border with Turkey, an IS offensive in the Aleppo province left at least another 100,000 people stranded, rights groups and activists said.

IS fighters cut a key road between the rebel towns of Azaz, close to the Turkish border, and nearby Marea, journalist Maamoun Khateeb told AFP from Azaz.

"This is a disaster," Khateeb said, adding that some 15,000 people were now besieged in Marea.

"We are terribly concerned... about the estimated 100,000 people trapped between the Turkish border and active front lines," said Pablo Marco, regional operations manager for Doctors Without Borders (MSF).

IS has recently been losing large parts of the territory straddling Syria and Iraq over which it proclaimed a "caliphate" with Abu Bakr al-Baghdadi as its head two years ago.

It had tried to remain on the offense however and conducted devastating bomb attacks, including in Baghdad and in towns that are bastions of the Syrian regime's Alawite minority.

The unfolding offensives and human tragedy came as world powers try to salvage a shaky ceasefire between the regime and non-jihadist rebels agreed in February to boost efforts to end a conflict that has killed more than 280,000 people.

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