"Our lorries got caught in the fighting. We will have talks with both parties (the military and the rebels) and try again tomorrow," Gordon Weiss, the spokesman of the UN Colombo office said.
However, the military accused Liberation Tigers of Tamil Eelam (LTTE) rebels of forcing the return of the UN convoy.
"The LTTE fired artillery and detonated claymore mines to disrupt the food convoy," military spokesman Udaya Nanayakkara said.
Meanwhile, a pro-rebel website said "humanitarian officials in Vanni" blamed the troops for sabotaging humanitarian supplies by firing shells on the access route.
The website also said the troops had destroyed a bridge five days ago on the access route which was used by the UN convoy to the refugees in the rebel controlled area during the first week of October.
The UN said earlier Thursday that it tried to dispatch 750 metric tonnes of food to the IDPs in the rebel controlled area.
Officials from UN agencies say some 230,000 civilians have been forced out from their homes by the fighting between the two sides in the Kilinochchi and Mullaithivu districts -- the last two districts controlled by the rebels.
The UN agencies have expressed concern over the plight of the displaced who are facing severe shortages of food and shelter.
The government has accused the rebels of not permitting the civilians to proceed to the government controlled area where two demilitarized zones have been declared by the government.
Escalation of fighting in Kilinochchi is being seen as the most crucial in the conflict between the two sides.
The government claimed its troops had recorded a series of military victories over the rebels elsewhere in the Northern and Eastern provinces since 2006.