Gunmen and suicide bombers killed at least 84 people in southern Iraq in the deadliest attack by the Islamic State group since it lost second city Mosul, according to a new toll released on Friday.

Many of the dead in Thursday's attack near the city of Nasiriyah were Shiite Muslim pilgrims, some of them Iranian, officials said.

"The death toll has risen to 84 after the discovery of 10 more bodies at the scene of the attack," said Jassem al-Khalidi, health director for Dhiqar province, which has largely been spared the violence that has plagued northern and central Iraq.

"Another 93 people were wounded, many of them seriously," Khalidi told AFP.

The assailants struck at midday, opening fire on a restaurant before getting into a car and blowing themselves up at a nearby security checkpoint, officials said.

They left a trail of destruction, with charred bodies scattered on the ground near the burnt-out wrecks of cars, buses and trucks, an AFP correspondent reported.

The attack was quickly claimed by IS, which appears to be switching to insurgent attacks after suffering a string of setbacks on the battlefield.

UN envoy Jan Kubis condemned the "cowardly twin attacks... which resulted in numerous civilian casualties, including many pilgrims." 

Shiites have been the target of repeated attack by the Sunni extremists of IS who regard them as heretics.

The area targeted by Thursday's attack lies on a highway used by Shiite pilgrims from Iran and southern Iraq to travel to the shrine cities of Najaf and Karbala further north.