Taliban fighters have advanced in their fight against government forces on the capital of Afghanistan's southern province of Helmand, prompting many families to flee.
The battle near Lashkar Gah town came on Tuesday, three weeks after the armed group won its biggest fight since 2001, capturing the northern town of Kunduz and holding the city centre for three days.
"Helmand's capital appears to be under serious military pressure," a Western official told the Reuters news agency. "We're hearing reports about civilians fleeing in large numbers."
Mirza Khan Rahimi, the governor of the province, said heavy fighting had been going on for two days in the district of Gereshk to the north of the city. The fighting has threatened Highway One, the main transport artery linking the major southern city of Kandahar with Herat.
Farhad Dawary, head of the local Civil Societies Union, which represents non-government social organisations, said that after days of fighting, families were both fleeing to Lashkar Gah from outlying areas and trying to escape from the city.
"There is fear among the people in Lashkar Gah, there are lots of rumours the city might fall," he said.
Helmand province is one of the world's biggest centres of opium cultivation, with a complex mix of warring tribal groups and Taliban fighters creating a chronic problem for the Western-backed government.
Afghan government forces, which have taken on the bulk of fighting since international troops ended most combat operations last year, have struggled to contain the Taliban, which has stretched the army in a series of operations across the country.
Battle for Herat
As the battle continued near Lashkar Gah, there were also reports of heavy fighting in the Ghurian district near the major western city of Herat.
The Taliban raised their flag in the main district centre for a few hours before police reinforcements arrived and cleared them out, Herat police chief, General Abdul Majid Rozi said.
As the fighting flared, Afghan President Ashraf Ghani chaired a meeting of the National Security Council and ordered military forces to step up combat operations against the unrest.
Earlier this week, they were also reported to have overrun the district of Ghormach in Faryab province on the northern border with Turkmenistan.
The deteriorating security situation prompted US President Barack Obama last week to delay plans to pull American forces out of the country next year, with at least 5,500 troops now due to remain after 2017.