As many as 50,000 Iraqis in Fallujah face starvation and death as they are unable to leave the besieged city controlled by Islamic State of Iraq and the Levant (ISIL, also known as ISIS).

Lise Grande, a senior UN official, told Al Jazeera on Thursday that humanitarian conditions "have deteriorated in the last three months" and the city 70km west of Baghdad "could be facing a catastrophe.

"We are deeply worried about the situation. There have been few medical supplies and no re-supply of food in the last two or three months," Grande said, citing sources in Iraq.

READ MORE: Civilians flee ISIL-held territory in Iraq

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

Grande's comments followed a plea by New York-based Human Rights Watch (HRW) urging the warring parties "to make sure that aid reaches the civilian population".

The rights group said residents have reported that as many as 140 people, many elderly and children, have died over the past few months because of a lack of food and medicine.

Several people, including one entire family, were also reportedly executed by ISIL fighters for trying to leave Fallujah. The armed group has jailed more than 100 men for protesting against the execution of family members, HRW said.

'Soup made from grass'

It is impossible to verify the information independently with limited access to Fallujah, and as ISIL prohibits the use of mobile phones and the internet.

In one recent video that Baghdad-based activists provided to HRW, an unidentifiable woman said she is from Fallujah and that her children are dying because there is no rice, no flour - not even local dates - and the hospital has run out of baby food.

Reports have surfaced of people being forced to eat bread made from ground date seeds while drinking soup made from grass, HRW said. A sack of flour was being sold for $500 in Fallujah compared with $15 in the capital, Baghdad.

On March 24, the World Food Programme said it remained "concerned about the food security situation in besieged Fallujah, [where] many food items were unavailable in markets".

Human Rights Watch's Joe Stork said ISIL has shown "utter disregard for protecting civilians in conflict". He called on the armed group to allow civilians to leave, while also urging government forces to open routes for humanitarian aid.