Aircraft from the US, Britain, France and Australia have dropped parcels of food and water on the Iraqi town of Amirli, which is surrounded by Isis (Islamic State) militants.

Thousands of Shi'ite Turkmen have been stranded in the farming community about 105 miles north of capital city Baghdad for nearly two months.

On Sunday, Iraqi forces broke through to the town under threat from the jihadists. "Our forces entered Amerli and broke the siege," security spokesman Lieutenant General Qassem Atta told AFP.

The US military conducted "coordinated airstrikes" against Islamic State targets, as part of an effort to support the humanitarian operation, Kirby said.

Military operations will be limited to addressing the needs of the humanitarian crisis in Amirli and protect civilians trapped in the area, added Kirby.

The local inhabitants, the Shi'ite Turkmens decided to stay and fortify their town instead of escaping in the wake of the Islamic militant attack. The town is fortified with 15,000 trenches and armed positions.

Besieged by Isis

In June, Amirli fought off an attack and the town has been surrounded since mid-July.

Some locals claim that the Iraqi military effort to bring them food, water and aid has been insufficient, as the town is suffering from sweltering temperatures and a lack of electricity. The town's power station was razed to the ground by shelling from militants a few weeks ago.

"Residents are enduring harsh living conditions with severe food and water shortages, and a complete absence of medical services – and there are fears of a possible imminent massacre," UN high commissioner for human rights Navi Pillay told CNN.

Michael Knights, who studies Iraq and the Persian Gulf as a fellow of The Washington Institute, said US airstrikes will quicken the success of the relief effort on the ground.

About half of Amirli's population is aged 15 and under, while many others are elderly, sick or wounded, Knights said.

"They are remarkably vulnerable, and Isis are determined to kill as many of these people as possible," Knights said. "As the Nazis felt about the Jews, so Isis feels about the Shia Muslims."

Isis has called the Shi'ite Turkmen heretics and vowed to destroy them.

Turkmen are descendants of a Turkic-speaking, traditionally nomadic people, who share culture ties with Turkey. There are Sunni and Shi'ite Turkmen in Iraq, accounting for up to 3% of Iraq's population.