Iraqi security forces and Shia militiamen on Sunday broke a six-week siege imposed by the Islamic State extremist group on the northern Shia Turkmen town of Amirli, following U.S. airstrikes against the Sunni militants' positions, officials said.

Army spokesman Lt. Gen. Qassim al-Moussawi said the forces "reached" the town, but gave no details. Turkmen lawmaker Fawzi Akram al-Tarzi said they entered the town from two directions and were distributing aid to residents.

About 15,000 Shiite Turkmens were stranded in the farming community, about 170 kilometres north of Baghdad. Instead of fleeing in the face of the Islamic State of Iraq and Syria's rampage across northern Iraq in June, the Shia Turkmens stayed and fortified their town with trenches and armed positions.

Residents succeeded in fending off the initial ISIS attack in June, but Amirli has been surrounded by the militants since mid-July. Many residents said the Iraqi military's efforts to fly in food, water and other aid had not been enough, as they endured the oppressive August heat with virtually no electricity or running water.

Nihad al-Bayati, who had taken up arms with fellow residents to defend the town, said some army units had already entered while the Shia militiamen were stationed in the outskirts. He said residents had fired into the air to celebrate the arrival of the troops.

"We thank God for this victory over terrorists," al-Bayati told The Associated Press by phone from the outskirts of Amirli. "The people of Amirli are very happy to see that their ordeal is over and that the terrorists are being defeated by Iraqi forces. It is a great day in our life."

U.S. and other countries air drop aid

On Saturday, the U.S. conducted airstrikes against the Sunni militants and air-dropped humanitarian aid to residents. Aircraft from Australia, France and Britain joined the U.S. in the aid drop, which came after a request from the Iraqi government.

The Pentagon's press secretary, Rear Adm. John Kirby, said military operations would be limited in scope and duration as needed to address the humanitarian crisis in Amirli and protect the civilians trapped in the town.

The ISIS extremist group, also known as  Islamic State, has seized cities, towns and vast tracts of land in northeastern Syria and northern and western Iraq. It views Shias as apostates and has carried out a number of massacres and beheadings — often posting grisly videos and photos of the atrocities online.

The U.S. started launching airstrikes against the Islamic State extremist group earlier this month to prevent the insurgents from advancing on the Kurdish regional capital Irbil and to help protect members of the Yazidi religious minority stranded on Mount Sinjar, in Iraq's northwest, where U.S. planes also dropped humanitarian aid.

The U.S. also launched airstrikes near Mosul Dam — the largest in Iraq — allowing Iraqi and Kurdish forces to retake the facility, which had been captured by Islamic State fighters.

Earlier Saturday, the U.S. Central Command said five more airstrikes had targeted Islamic State militants near Mosul Dam. Those attacks, carried out by fighter aircraft and unmanned drones, brought to 115 the total number of airstrikes across Iraq since Aug. 8.