Kurdish fighters break key ISIS supply route in fight for Sinjar

SINJAR, Iraq -- American war planes hammered the forces of ISIS in Iraq Thursday, opening an offensive the Pentagon hopes will be a breakthrough against the Islamic extremists occupying much of Syria and Iraq.

U.S. airstrikes back Kurd offensive to reclaim Sinjar from ISIS

Kurdish Peshmerga troops, backed by 36 American airstrikes, moved to take the town of Sinjar. They seized part of a highway used by ISIS to ferry supplies from Raqqa, its stronghold in Syria, to Mosul, an Iraqi city of more than 1 million people.

The battle to reclaim Sinjar began in the air. U.S. airstrikes pounded suspected ISIS targets throughout the day. Thick smoke hung over the city, and ISIS fighters lit banks of tires to try and block the bombers' visibility.

Dug in on the mountainside, Kurdish forces searched for targets, passing the coordinates back to U.S. advisers.

It's one of the forward fighting positions where they're helping to pick targets for airstrikes. Soldiers there told CBS News that with aircraft overhead all the time, sometimes it's just five minutes from the moment they call in the strike to the time it's delivered.

Kurdish fighters are so close to the ISIS militants, they can hear their conversations on simple two-way radios.

Sniper Mazan Maraq is watching the enemy. "They're inside houses," Maraq said. "They move from house to house, they're behind the rubble."

Maraq and his family fled Sinjar when ISIS militants overran the city 15 months ago.

Tens of thousands were uprooted in the terror that followed as ISIS murdered, raped and enslaved members of the Yazidi religious sect.

Yazidi villagers describe ISIS atrocities

The 22-mile stretch of highway that Kurdish forces took control of today breaks a key ISIS supply route, but the fight is only starting. As the day wore on, Kurdish soldiers spotted more ISIS militants on the move, and scrambled into position.

Maraq said he hopes ISIS will be defeated and his family can return home.

The fight is going to go house to house. Peshmerga soldiers told CBS News they are expecting snipers, car bombs, and booby traps not only on the roadside, but also inside buildings as they push further into the city.