UN Iraq envoy Nickolay Mladenov warned in a statement Saturday that the town of Amerli to the north of Baghdad has been cut off from the rest of government-held territory since "Islamic State" (IS) swept through the province in a lightning offensive in early June.

He said the 20,000 citizens of Amerli, who are mostly Shiite, face a "desperate" situation in the face of Sunni extremists that, "demands immediate action to prevent the possible massacre of its citizens."

"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," he said.

Prime minister designate Haidar al-Abadi promised aid for the town on Saturday, calling for the provision of "all types of military and logistical support for Amerli."

Iraq's government, supported by Kurdish forces and US airstrikes, is fighting IS militants from positions in the north of the country.

On Friday, Iraq's most powerful Shiite cleric, Grand Ayatollah Ali al-Sistani, who is revered by millions, sought to bring attention to Amerli's plight.

"Amerli suffers from a tight blockade in place for two months," and has been defended by "heroic men with limited weapons and ammunition and a severe shortage of food items," Sistani said in remarks read on his behalf.

Bomb attacks kill dozens

Meanwhile, bombings in Baghdad and the northern city of Kirkuk killed at least 34 people on Saturday as the government continued to investigate a deadly attack on a Sunni mosque the day before.

Security officials said the attack on the mosque on Friday, in a village in Diyala province, began with a suicide bombing at the entrance, followed by gunfire as worshippers rushed out of the mosque. At least 70 people were killed in the attack with at least 20 others said to have been seriously injured.

The violence comes as Iraq faces one of its deepest political crises in a decade. Deputy Prime Minister Saleh Mutlaq and Parliament Speaker Salim al-Jibouri, both Sunni, have pulled out of talks with the main Shiite alliance until results of an investigation into the mosque killings are announced.

If talks were to stall, it would be a major hurdle for Shiite prime minister-designate al-Abadi, who is looking to unite Sunni and Shiite lawmakers in a new government by September 10.

hc/av (Reuters, AFP, AP, dpa)