Nikolay Mladenov, the UN secretary general’s representative in Iraq, said immediate action is needed to “prevent the possible massacre” of civilians in the northern town of Amerli.
He urged the Iraqi government and other countries to implement concerted action to end the siege in Amerli, 177 kilometres from the capital, Baghdad.
“The town is besieged by ISIL and reports confirm that people are surviving in desperate conditions,” he said in a statement.
“I urge the Iraqi Government to do all it can to relieve the siege and to ensure that the residents receive lifesaving humanitarian assistance or are evacuated in a dignified manner.
“Iraq’s allies and the international community should work with the authorities to prevent a human rights tragedy.”
The town has a population of nearly 18,000 Turkmen Shiites, who have been cut off from food and water supplies after Islamic State fighters launched an offensive in the Salaheddin province in early June.
Local media reports say government helicopters have been able to drop supplies infrequently but added that the government is still facing difficulty in reaching civilians trapped by the fighting.
Dr Ali Albayati at Turkmen Saving Foundation said many children are dying in the town due to dehydration and disease.
He says children have only been eating one meal every three days.
“It is a humanitarian disaster. Twenty-thousand people in Amerli are fighting off death.
“After the attack of Mosul, all the Shiite Turkmen villages around Amerli were captured by the Islamic State. They killed the people and displayed their bodies outside the village,” he told the BBC.
“We are depending on salty water, which gives people diarrhea and other diseases. Since the siege started more than 50 sick or elderly people have died,” he said.
Earlier this month, ISIS attacked Mount Sinjar, home to tens of thousands of the Yazidi ethnic minority. The fighting forced many from their homes, with an estimated 500 people killed during the siege.
Iraq’s most influential cleric, Grand Ayatollah Ali al-Sistani used his speech atfer Friday prayers to voice concern over the situation in Amerli.
British foreign secretary Philip Hammond on Friday offered in-principle support for an international operation to help people in Amerli, saying the government would be closely watching events.
Devastation in Iraq’s Kirkuk following car bombs
It comes on a day when dozens have died after three near-simultaneous car bombs exploded in the northern Iraqi city of Kirkuk on Saturday, killing 21 people and wounding 118, a senior police officer and a doctor said.
Two of the bombs exploded near buildings under construction that were used as observation positions by security forces, while the third struck the entrance to a market.
The bombings come as Iraqi federal and Kurdish security forces battle a jihadist-led militant offensive that was launched in June and has overrun large areas of five provinces.
In the early days of the onslaught, Iraqi soldiers left their positions in oil-rich Kirkuk province, the capital of which is the city of the same name.
This cleared the way for Kurdish forces to take control of it and other disputed northern areas that they have long wanted to incorporate into their autonomous region, over the strong objection of Baghdad.