Islamic State group fighters launched suicide attacks Wednesday at US-backed Syrian forces in a desperate bid to defend their last scrap of territory after 3,000 of their fellow jihadists surrendered.

Despite the counterpunch the Kurdish-led Syrian Democratic Forces said IS is living its "final moments" after three nights of thunderous shelling on its final holdout in eastern Syria near the Iraqi border.

AFP correspondents heard air strikes and artillery fire near the frontline after night fall Wednesday, on a fourth night of bombardment.

IS once ruled over millions in a swathe of Syria and Iraq, but it has since lost all that territory except for a riverside slither in the village of Baghouz near the Iraqi border.

Thousands of men and women have poured out of the pocket in recent weeks, hampering an advance by the SDF, which has paused its offensive multiple times to allow evacuations.

Supported by air strikes by the US-led coalition, the SDF resumed shelling on Sunday.

They unleashed a deluge of fire on jihadist outposts for three nights in a row, engulfing their makeshift encampment in a ravaging blaze.

"IS's final moments have started," SDF official Jiaker Amed told AFP Wednesday.

Clashes flared as the SDF worked to thwart any IS fightback.

Jihadists "launched two counterattacks today -- one in the morning and another in the afternoon", an SDF official told AFP.

"The second one was much stronger" and was launched under the cover of smoke caused by bombing, he said.

The official said jihadists were using suicide bombers but his force intercepted them before they reached their target.

The jihadists "made no progress and they were stopped," he said.

- 'Final hour' -

Inside Baghouz, the crackle and thud of gunfire and shelling rang out from the encampment as plumes of thick black smoke rose over the bombed-out IS bastion.

Amid the rubble, three SDF fighters lobbed a salvo of mortar shells towards the IS pocket, hours after the first attempted counterattack at daybreak under the cover of a dust storm.