"Peshmerga forces have reached Mount Sinjar, the siege on the mountain has been lifted," Masrour Barzani, head of the Iraqi Kurdish region's national security council, told reporters from an operations center near the border with Syria on Thursday.
The assault, backed by US-led air strikes, ended the months-long ordeal of hundreds of people from Iraq's Izadi minority, who had been besieged on the mountain since ISIL stormed Sinjar and other Kurdish-controlled parts of northern Iraq in August, he said.
"All those Yazidis that were trapped on the mountain are now free," Barzani said, using another term for Izadis. He added that the Peshmerga had not yet begun to evacuate them.
He said 100 ISIL fighters had been killed - a claim that could not be independently verified, according to Al Jazeera.
Kurdish Peshmerga soldiers began their offensive on Wednesday to break the armed group's siege of the mountain and the town of Sinjar.
Lieutenant General James Terry, head of the US-led campaign against ISIL, said more than 50 air strikes in recent days "have resulted in allowing those (Kurdish) forces to maneuver and regain approximately 100 square kilometers of ground" near Sinjar.
The capture of Sinjar by ISIL fighters and the plight of the mostly Izadi population there was cited by President Barack Obama as one of the reasons for the US military intervention in Iraq.
The US and allied aircraft have carried out 1,361 raids against ISIL since bombing began on August 8, Terry said.
The advance of the ISIL fighters had been halted and the group was having difficulty moving and communicating as a result of the air campaign, he said.
"I think we've made significant progress in halting that progress (by ISIL)," Terry said.
In another claim of success in the battle against ISIL, US officials said on Thursday that coalition strikes have killed several of the group's senior leaders since mid-November.