The food situation for 60,000 civilians trapped in the besieged Iraqi city of Fallujah is extremely worrying and likely to deteriorate unless aid gets into the city, the U.N. World Food Program said Monday.

The Iraqi army, police and Iranian-backed Shiite Muslim militias -- backed by airstrikes from a U.S.-led coalition -- have maintained a near total siege on the Islamic State group-held city, which is located 30 miles west of Baghdad, since late last year.

"As the siege continued in Fallujah for the third consecutive month, no sign of improvement was recorded in March; food prices remain extremely high, and stocks in shops and households are depleting. In March, the price of wheat was six times more expensive than in December," the report said.

"For the third consecutive month, respondents from Hay Alwahda sub-district reported that shops and markets had exhausted all food supplies including wheat, sugar, rice, vegetable oil and lentils," the report said.

The report was based on a mobile phone survey conducted in March. But it said reaching respondents had become increasingly difficult and very limited information was available, especially as armed opposition groups had shut down transmitter towers to stop people using mobile phones.

"Aid has not reached Fallujah since the government recaptured nearby Ramadi in December 2015, with supply routes cut off by Iraqi forces and the armed groups preventing civilians from leaving," the report said.

There were reports that people wanting to leave the city and seek safety were unable to do so, it said.

Last week a report from New York-based Human Rights Watch said desperate residents were making soup from grass and using ground date seeds to make flour for bread.