BAGHDAD, Iraq (CNN) -

As violence continues to wrack Iraq, another ethnic slaughter may be in the making by Sunni extremists from ISIS.

ISIS fighters have besieged the ethnic Turkmen Shiite town of Amerli in the north for two months, and its fewer than 20,000 residents are without power and running out of food, water and medical supplies.

"The situation of the people in Amerli is desperate and demands immediate action to prevent the possible massacre of its citizens," said Nickolay Mladenov, the U.N. secretary-general's special representative for Iraq.

He said the suffering was "unspeakable" and demanded that the Shiite majority Iraqi government "relieve the siege" on Amerli.

Small town fights ISIS

About 5,000 families live in Amerli, which has been under siege for 70 days, according to Dr. Ali Albayati, head of the Turkmen Saving Foundation. He told CNN the town is running without electricity, is out of medicine and can only turn to wells for water.

Nearly three dozen villages surrounding Amerli are already under ISIS control, Albayati said. The people of Amerli are relying on the Iraqi government to take them out by helicopter or support them with food drops, Albayati said. In the past 10 days, he added, only one flight has delivered food.

Surrounded on four sides, the 17,400 residents have had to defend themselves with only the help of local police, said Masrwr Aswad of Iraq's Human Rights Commission.

Their situation echoes the ordeal of Iraq's ethnic Yazidis, whose plight after they were forced to flee into the mountains to escape militants ISIS triggered U.S. aid drops and the first U.S. airstrikes against ISIS.

ISIS has targeted Shiite, Christian and other minority communities with shocking violence, as it has advanced across Iraq.

Bombings, mosque shooting

Suicide bombers targeted the Interior Ministry intelligence headquarters in Baghdad on Saturday, killing at least four people and injuring 35 others. In Kirkuk, a series of three car bombs and a roadside bomb killed at least 20 people.

ISIS had warned on Friday there would be revenge for the killing of 50 of its members in a battle in Jalawla, Iraq. ISIS specifically promised to retaliate against the Kurdish Peshmerga forces.

The bombings came as the death toll rose to 70 from an attack on Sunni Muslims a day earlier at a mosque in northeast Iraq, when suspected Shiite militiamen opened fire on worshipers.

The mosque attack threatened to derail efforts to form a new, inclusive government -- something world leaders have said is a must if the country hopes to defeat Islamic militants.

Iraqi authorities did not immediately identify the attackers, but Sunni politicians have put the blame on Shiite militias.

Outraged Sunni lawmakers withdrew from negotiations to form a new government, saying they would not return until those behind the attack were arrested, two party officials told CNN.

U.S. President Barack Obama has authorized targeted airstrikes to protect U.S. personnel in Iraq -- including military advisers -- as well as minorities being brutalized by ISIS.

And U.S. officials have said that Washington is mulling the possibility of going after ISIS fighters in their stronghold in eastern Syria.