The United Nations on Friday called for "unhindered humanitarian access" to people fleeing the last pocket of ISIS militants in eastern Syria.
US-backed forces in the area responded that they had asked for help from the UN after securing safe corridors for tens of thousands to flee the fighting.
In the past week alone, the UN says more than 10,000 people have fled from the conflict zone to Al-Hol, where the main camp for people displaced by the fighting against IS is located.
"Humanitarian actors have collectively requested forces in control of the area to designate a transit site en route for Al-Hol where life-saving assistance can be provided," said Andrej Mahecic, spokesman for the UN refugee agency (UNHCR).
So far the request "remains unanswered", he told journalists in Geneva.
The Kurdish-led Syrian Democratic Forces, who control the area around Al-Hol, immediately responded that they had never received such a request from the UN.
"On the contrary, we have long expressed our position that we need assistance, especially UN aid to support us on this issue, which is beyond the capability of the" Kurdish authorities, SDF spokesman Redur Khalil told AFP.
In Al-Hol, "there is malnutrition, a lack of medical supplies, tents, and blankets", he added.
Over the past month, the SDF were able to secure the exit of 20,000 Iraqis - mostly women and children - from IS-held territory, as well as hundreds of Syrians and non-Iraqi foreigners.
Backed by a US-led coalition, the SDF are battling the last shreds of the IS "caliphate" near the town of Hajin in the Euphrates River valley.
The UNHCR says families fleeing the Hajin enclave describe a harrowing journey, "wading through mine fields and open fighting".
Once reaching the SDF positions, "they describe being herded into open trucks and having to endure another arduous journey in winter weather northwards to Al-Hol camp. Little or no assistance is provided en route to the hungry and cold people, the vast majority of whom are women and children", a UNHCR statement said.
Since early December at least 29 young children and newborns died on their journey or shortly after arrival at the camp, according to the UN.
"We reiterate our calls for unhindered humanitarian access. It is vital that our teams are able to deliver life-saving humanitarian assistance, especially during this harsh winter period," Mr Mahecic said.
The Syrian conflict has killed 360,000 people and led millions to flee their homes since starting with the brutal repression on anti-government protests in 2011.
