Bodies on the streets as fighting traps Lashkar Gah residents

"The Taliban will have no mercy on us and the government won't stop the bombing."

The resident of Lashkar Gah in southern Afghanistan is one of thousands trapped or fleeing for their lives as fighting for control of the city rages between militants and government forces.

The BBC is not naming some interviewees in this article for security reasons.

"There are corpses on the roads. We do not know if they are civilians or the Taliban," the man told the BBC Afghan service in an interview on Whatsapp. "Dozens of families have fled their homes and settled near the Helmand river."

Other terrified locals told the BBC they had seen bodies lying in the streets.

Capturing the besieged Helmand provincial capital would be of huge symbolic value to the insurgents as they continue their rapid advance after the pullout of foreign forces. Helmand was the centrepiece of the US and British military campaign.

The United Nations and other agencies are warning of a worsening humanitarian crisis. At least 40 civilians have been killed in Lashkar Gah in the past day, the UN said on Tuesday.

The Afghan army urged civilians to leave Lashkar Gah ahead of a major offensive against the Taliban, the hardline Islamist group that was driven from power by US-led forces 20 years ago.

Elsewhere in the south, Taliban are trying to capture Kandahar, their former stronghold, and clashes have also intensified in Herat in the west.

Fighting has been continuing in Lashkar Gah for days, with the militants now reportedly in control of most districts.

"We are going through difficult days," a student in the city told the BBC. "The Taliban set fire to the ground and government air forces to the skies."

Another man said on Sunday: "The Taliban can be seen on the city's roads. The presence of the Taliban has astonished people here.

"Shops are closed, and government military vehicles are lying destroyed in the middle of the road. The war continues within a few metres of the governor's office and the National Security Directorate.

"The central government said recently they had deployed new commandos to Lashkar Gah, but we didn't see them."

Hundreds of Afghan reinforcements have since reportedly been deployed to the city.