The UN's children's agency warned Tuesday that up to 20,000 civilians, mainly women and children, could be trapped by harsh fighting in the Syrian town of Qusayr.
"The situation is desperate," UNICEF spokeswoman Marixie Mercado told reporters in Geneva.
Her comments came as the battle for Qusayr, in central Homs province, raged for a third day after President Bashar al-Assad's forces and allies launched an offensive to reclaim the town more than a year after rebels seized it.
UNICEF believes that between 12,000 and 20,000 civilians remain trapped in the town that used to count some 30,000 inhabitants, Mercado said.
"What are the most urgent needs? Protection," she said, pointing out that those who remain "need to be protected from the bombardment, from the fighting that's going on in the city right now."
Mercado said that most of the civilians stuck in Qusayr were believed to be women and children, as were those who had managed to flee.
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She said it remained unclear where the men who used to live in the city were.
UNICEF did not have any staff in the city, but was along with other organisations helping around "500 families made up of women, children and elderly" who had fled from Qusayr and nearby villages in recent days to Hasiaa, near Homs.
"They are joining an additional 1,144 families who had previously fled Qusayr, where fighting has flared over the past month," she said, pointing out that for those who have left the city, there were also "just enormous needs right now."
"Many of the families left at night with little or no possessions," she said, adding that UNICEF and others were providing them with clothing, water and sanitation.
The Syrian Observatory for Human Rights, a Britain-based watchdog, has said some 25,000 civilians were still trapped in Qusayr, and described the rebel response to the assault on the city as "fierce."
According to the Observatory, Hezbollah fighters from neighbouring Lebanon are leading the attacks on the ground while Assad's warplanes carry out air strikes.
Assad and Hezbollah have made reclaiming Qusayr, which lies between the Syrian city of Homs and Tripoli in northern Lebanon, a priority in its fight to turn the tide against the two-year insurgency.