ARBIL - Iraqi Kurdish forces were working to clear bombs planted by the Islamic State group in Sinjar, where a grave believed to hold dozens of the jihadists' victims was found Saturday.

The bombs must be removed before the northern town's mainly Yazidi residents -- members of a minority group who were targeted in a brutal campaign of massacres, enslavement and rape by IS -- can return and begin rebuilding their lives.

Kurdish regional president Massud Barzani on Friday announced the "liberation of Sinjar", a day after the launch of a major ground operation to drive out the jihadists. "Until now, we defused 45 bombs and a car bomb," said Sulaiman Saeed, a member of the autonomous Kurdish region's peshmerga forces who works in explosives disposal.

"Bombs are widespread in houses," Saeed said, adding that some 20 tonnes of explosives were found in a bomb-making factory, while they also discovered 20 barrels of explosives.

"Now that they've seized Sinjar, or freed Sinjar, the next phase is to go back and clear it," Colonel Steve Warren, spokesman for the international operation against IS, told a news conference on Friday. "That will take a while, that will probably take a week, 10 days, maybe even two weeks, depending on the complexity of the minefields and obstacles that (IS) left behind," Warren said.

But bombs are not the only obstacles to a return by residents, as many houses and shops were smashed during the fighting. With the town retaken from IS, new evidence of the jihadists' horrific abuses is beginning to emerge.

Based on information from young women who witnessed the executions and were enslaved by IS but later escaped, officials on Saturday found the site of a mass grave believed to hold dozens of Yazidi women killed by the jihadists. Miyasir Hajji, a local council member for Sinjar, told AFP that the grave on the edge of the town, which has not yet been excavated, is thought to contain the bodies of 78 women aged from 40 to around 80.

"It seems that the (IS) terrorist members only wanted young girls to enslave," Hajji said, referring to the jihadists using women as sex slaves who can be bought and sold.

Mahma Khalil, the local official responsible for the Sinjar area, confirmed that the mass grave had been found, and estimated it held some 80 victims. The ground operation to drive the jihadists out of Sinjar, which began Thursday morning, was led by peshmerga forces and also involved Yazidi fighters, with support from US-led air strikes.

They were able to cut Highway 47, one of IS's main supply routes linking territory it holds in Iraq and Syria, in the Sinjar area on Thursday, and moved into the town the following day. IS overran Sinjar in August last year, forcing thousands of Yazidis to flee to a mountain overlooking the town, where they were trapped by the jihadists.

The United Nations has described the attack on the Yazidis as a possible genocide. Aiding the Yazidis, whose unique faith IS considers heretical, was one of Washington's main justifications for starting its air campaign against the jihadists last year.