"More and more children in this city are being killed, injured and denied their essential needs due to the fighting," said Shahida Azfar, UNICEF Regional Director for the Middle East and North Africa.

"Extraordinary efforts must be taken to protect them. The siege must stop," she added in a statement.

Rebel-held Misrata is surrounded by Libyan government forces and has been the scene of heavy bombardments for more than a month, with fighting also reaching the city centre.

UNICEF warned that tens of thousands of children were at risk, adding that it had verified that at least 20 children as young as nine months were killed by shrapnel from mortar and tank fire as well as bullets.

Nearly all the deaths occurred in the past 20 days and most of the victims were less than 10 years old.

"Intensified fighting and indiscriminate shelling has led to an increased number of children being killed in Misrata, with many others lacking food and safe water, and traumatised from the atrocities they have witnessed," the agency said.