Civilians were urged by the Afghan army to evacuate the southern city of Lashkar Gah as security forces prepare an operation against the Taliban.
Fighting in the area has already led to significant civilian injuries and deaths, according to the UN mission in Afghanistan.
At least 40 civilians have been killed and more than a hundred injured in the last 24 hours, the UN mission said.
It was mostly due to a Taliban ground offensive and army airstrikes, the UN mission added, calling on parties to do more to protect civilians, warning of a potential catastrophe.
The Taliban has gained momentum and territory in Afghanistan as the US and NATO finish withdrawing their troops.
UN envoy Deborah Lyons met with Afghanistan’s foreign minister and “expressed deep concern on the increasing number of Afghan civilians being killed, injured and displaced, especially when attacks are unleashed against cities.”
General Sami Sadat, the highest ranking army officer in southern Afghanistan, asked people to leave their homes so the army could face the Taliban.
“Leave as soon as possible so that we can start our operation,” Sadat warned.
Sefatullah, head of local radio Sukon, told AFP that “the fighting was intense this morning” in Lashkar Gah, adding that Taliban positions in the city had been targeted with airstrikes.