BAGHDAD (Reuters) - Human Rights Watch (HRW) on Thursday called on Iraqi forces besieging the Islamic State-held Falluja to allow aid to reach tens of thousands of residents facing acute shortages of food and medicine.

File photo of a tank of the Iraqi army is seen on the outskirts of the city of Falluja, Iraq May 19, 2015. REUTERS/Stringer

The Iraqi army, police and Iranian-backed Shi’ite Muslim militias - backed by air strikes from a U.S.-led coalition - have maintained a near total siege on Falluja, located 50 km (30 miles) west of Baghdad, since late last year.

Desperate residents are making soup from grass and using flour from ground date seeds to make bread, New York-based HRW said in a report. Food, when available, costs up to 50 times the normal price.

“The people of Falluja are besieged by the government, trapped by (Islamic State), and are starving,” said Joe Stork, HRW’s deputy Middle East director. “The warring parties should make sure that aid reaches the civilian population.”

Falluja - a long-time bastion of Sunni Muslim jihadists - was the first Iraqi city to fall to Islamic State, in January 2014, six months before the group swept through large parts of northern and western Iraq and neighboring Syria.

Tribal sheikhs from Anbar province, where Falluja is located, held a news conference in Amman on Thursday to press the Iraqi government to find a way to lift the siege and get aid to residents stranded inside.

HRW also called on Islamic State to allow food and medicine into the city and to permit residents to leave. Iraqi and U.S. officials have said they are worried the insurgents would confiscate any aid sent to Falluja.

Defense ministry spokesman Naseer Nuri accused Islamic State of using civilians to obstruct the advance of Iraqi forces. “The real siege is not by Iraqi forces,” he said.

“The Iraqi forces are liberating, they want to liberate the city’s residents who have been held hostage by Daesh (Islamic State) for more than three years. Daesh is the one really besieging Falluja.”

Nuri said Iraqi forces had opened three corridors for civilians to flee but alleged that the militants had barred them from leaving.

BLEAK PICTURE

HRW, which has not had access to Falluja, said it relied largely on activists in Baghdad to communicate with residents directly or through people in contact with them.

“The humanitarian picture in Falluja is bleak and getting bleaker,” said Stork. “Greater international attention to the besieged towns and cities of the region is needed or the results for civilians could be calamitous.”

Since recapturing Ramadi - a further 50 km to the west - from Islamic State in December, Iraqi authorities have not made clear whether they will attempt to take Falluja soon or leave it contained while the bulk of their forces head north towards Mosul, the largest city under the militants’ control.

The humanitarian crisis has made recapturing Falluja from Islamic State a priority, Nuri said, but added that the timing was up to military leaders.

In the past two weeks, Iraqi forces backed by coalition air strikes have retaken significant parts of Hit, an important town 50 km northwest of Ramadi, and three villages in the Makhmour area that is set to be a key staging ground for a future assault on Mosul.

Shi’ite militias, which played a central role in offensives before Ramadi, have been largely sidelined in the predominantly Sunni provinces of Anbar and Nineveh, where Mosul is located, to avoid aggravating sectarian tensions.

But a spokesman for Asaib Ahl al-Haq, one of the most powerful Iranian-backed militias, told Reuters on Wednesday the group was prepared to enter Falluja, which he said Islamic State was using to launch bomb attacks in Baghdad.

“We must cut off the head of the snake - Falluja - if we want to preserve the security and stability of Baghdad,” he said.