Shelling lights up the sky over Baghouz, the last ISIS pocket in Syria

Special report: Campbell MacDiarmid witnesses the finale of the battle to wrestle the last territory from the militant group

As the sun set over the final bastion of ISIS territory in Syria, an inferno was raging inside the encampment where the group's remaining diehards were making a suicidal last stand against the encircling US-backed Syrian forces.

After four years of international efforts to push back the militants in Iraq and Syria, and a month of moving civilians and surrendering ISIS fighters from Baghouz in northern Deir Ezzor Province, the Kurdish-led Syrian Democratic Forces (SDF) announced a final push to clear the last ISIS hold on Friday.

The "stronghold" now measures just 700 square metres.

The status of the group’s self-declared Islamic State is a far cry from 2014, when it controlled lands stretching from the gates of Baghdad to the hills of Raqqa.

Its fighters once held territory estimated to be the size of Jordan, under which about 8 million people were subjected to brutal rule in the "caliphate" declared by ISIS leader Abu Bakr Al Baghdadi from a Mosul pulpit in 2014.

Officials expect the decisive battle in Baghouz to end soon, but not before they face thousands of planted mines, surprise attacks from a network of tunnels and a final wave of suicide bombers.

Advancing forces repelled an ISIS counter-attack shortly after the offensive began on Friday evening.

"Within a few days they'll be finished," Adel Judi, a commander with the Kurdish YPG militia that forms the backbone of the SDF, told The National on a hilltop overlooking Baghouz.

By Saturday night, all that remained were towering pillars of billowing black smoke. Under that shroud, the tiny cluster of hamlets and farmland that make up Baghouz had been burning since an ISIS ammunition dump caught alight earlier in the day.

As unseen coalition jets roared in the starry night sky, streams of tracer bullets tore into the remnants of Baghouz, where mortars, rockets and light arms were also being fired.

Explosion followed explosion in the encampment as incoming shells and burning munitions detonated.

The lack of tracer fire coming out suggested that anyone surviving behind ISIS lines was probably hunkered down in trenches and tunnels.

It was the fiercest night-time fighting from SDF's operations to regain Deir Ezzor in eastern Syria.

For the Kurdish fighters who fought ISIS since the 2014 battle for Kobane, where a small number of them defended the northern Syrian city in view of the Turkish border, there was little sympathy for the plight of those inside.

On a hilltop, Cdr Judi watched the battle with satisfaction, despite the shrapnel from an old wound in one of his eyes blighting his vision.

The burly, veteran fighter for the YPG had survived many battles with this hated enemy.

“We starved in Kobane and now ISIS are in tents,” he said as he spoke to his men on the front line, some about 50 metres from the extremists.

A mixture of Kurdish and Arab fighters, they were also jubilant at the prospect of a decisive victory over a foe that once posed a deadly threat to the Kurds.

“Laurence the Arab, how are you doing?” Cdr Judi said into his radio.

“If I felt any better it would be illegal,” came the reply over the handset.

“Burn, burn!” shouted another voice.

Backed against a bend in the Euphrates River, with Syrian government forces waiting on the far bank, there would be no escape for these ISIS fighters.

“Either they will die or they will go to the river and die,” Cdr Judi said.

With his men advancing cautiously there had been few coalition air strikes, he said, although this would shortly change.

About 15,000 people had fled the pocket in the past month, but the last women evacuated by the SDF on Thursday said there were more inside.

Also of concern was the possible presence of western hostages believed to be still held by ISIS.

Recent reports indicate that at least one has been seen alive by those who had been moved from Baghouz.

As of Saturday afternoon, there had been fatalities on the SDF side with at least seven of the force’s fighters wounded.

“There are martyrs but at this stage we cannot say more,” SDF commander Adnan Afrin said.

Earlier in the day, an ISIS thermal rocket hit an armoured vehicle carrying YPG media personnel, wounding two severely.

As the SDF fighters continued firing into the darkness, the roar of the jets intensified. Then came the whine of a strike and an enormous fireball rose above the ISIS posts.

The shockwave followed shortly after, causing a palpable thump to the chest from a kilometre away.

Any ISIS members still alive would be lucky to last the night. And even if they did, it was clear that their fate was already written.