Government forces on August 25 pushed the Islamic State group out of Qayyarah, considered strategic for a planned offensive against the jihadists' last Iraqi stronghold of Mosul further north.
Qayyarah had been "inaccessible for over two years", the UN World Food Programme (WFP) said in a statement.
"The people of Qayyarah... are suffering extreme hunger with scarce access to food supplies," said WFP's country director for Iraq, Sally Haydock.
WFP said the food delivered in the past week included dates, beans and canned food as well as rations containing lentils, rice, flour and vegetable oil, enough to last for a month.
The town is "in a dire state" with "black smoke" rising from oilfields around it that were set ablaze by the jihadists during fighting, WFP said.
"All of its shops were either destroyed or closed and food stocks were running dangerously low with people surviving only on wheat from the recent harvest," it said.
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"Safe drinking water, electricity and medical services remain nearly impossible to access," it added.
The UN food agency said it had also distributed food to "almost 2,000 displaced people living in camps and with host families in areas surrounding Qayyarah".
Located on the Tigris river, Qayyarah was retaken in a three-day operation led by Iraqi special forces backed by US-led coalition air strikes.
Its capture is part of a plan by Iraqi forces to drive IS from their last stronghold in Iraq in Mosul, 60 kilometres (35 miles) away.
The United Nations refugee agency UNHCR warned last month that a Mosul offensive could displace another 1.2 million people.
Around 3.4 million people have already been forced to flee their homes in Iraq by conflict since the start of 2014.
WFP said it was "scaling up its food assistance in Iraq ahead of the Mosul offensive but "urgently" needed $106 million to assist displaced families until the end of 2016.