Peshmerga fighters have been thwarted in attempts to evacuate thousands of people from Iraq’s Sinjar mountains due to landmines planted by ISIL extremists forced to yield control of the barren range.

Aided by U.S.-led coalition airstrikes, Kurdish troops seized the mountains during fighting Thursday, with Masrour Barzani, head of the Iraqi Kurdish region’s security council, declaring that 100 fighters from the Islamic State of Iraq and the Levant (ISIL) had been killed in the process.

“All those Yazidis that were trapped on the mountain are now free,” he added in reference to members of Iraq’s minority ethno-religious community forced to endure conditions on the plains for months.

But a military source in the Kurdish Central Command told Al Jazeera on Friday that despite the military success, it was not yet possible to bring trucks up the mountain with supplies because ISIL fighters had planted land mines along the road. Trucks will need to use the mountain’s dusty side roads, the source said, which could hamper an evacuation effort.

Thousands of Yazidis have been under siege since ISIL stormed Sinjar and other Kurdish-controlled parts of northern Iraq in August. As the Yazidis wait to be rescued, efforts to deliver aid to them suffered a further setback on Friday when a helicopter meant to bring supplies crashed while en route, Iraqi state television reported.

Kurdish peshmerga soldiers began their offensive on Wednesday to break ISIL’s siege of the mountain and the town of Sinjar and end the Yazidis’ months-long ordeal. The capture of Sinjar by ISIL fighters and the plight of the mostly Yazidi population there was cited by President Barack Obama as one of the principal reasons for U.S. military intervention in Iraq.

Lieutenant General James Terry, head of the U.S.-led campaign against ISIL, said that more than 50 air strikes were launched in recent days, allowing Kurdish forces to maneuver and regain approximately 40 square miles of ground near Sinjar. The U.S. and its coalition allies have carried out 1,361 air raids against ISIL since the campaign began on August 8, Terry said.

In another claim of success in the battle against ISIL, U.S. officials said on Thursday that coalition strikes have killed several of the group's senior leaders since mid-November.

Al Jazeera and wire services