Afghan police fear Taliban capture in Helmand's Sangin
Afghan police battling the Taliban in Helmand province say militants have laid siege to the police headquarters and supplies of ammunition are low.
Mohammad Dawood, police commander of Sangin district, said his officers had been surrounded, and, without urgent help, risked being "captured alive".
Helmand has seen fierce clashes in recent months, with large areas of the province being held by the Taliban.
Officials there have warned the whole of the southern province could fall.
In eastern Afghanistan, a suicide bomb attack on a US-Afghan patrol near Bagram airbase, in Parwan province, has killed five coalition soldiers, Reuters news agency reports.
Nato officials said the patrol had been targeted by an improvised device carried by a vehicle.
In a separate incident, the US embassy said a US citizen had been killed in the capital Kabul. Police told the BBC that a mullah killed Lisa Akbari while she was attending a local gym. The mullah has been arrested.
Helmand province is a key Taliban base and an area of opium cultivation - the province has seen some of the fiercest clashes between Nato-led forces and the Taliban.
More than 450 UK military personnel died during a 13-year combat mission in Afghanistan, including more than 100 in Sangin.
UK forces ended combat operations in October last year.
Police Commander Mohammad Dawood told the BBC's Mahfouz Zubaide via satellite phone: "The situation is very harsh... We haven't eaten for the past two days. If we don't get support in the next hour or so, our fighters will be captured alive."
"For the past two days we have been surrounded inside the police headquarters. No one can move out because the checkpoints along the roads are gone.
"We only have the police HQ under our control and have a battalion of the national army with us. The district office and the intelligence directorate are under enemy control."
A spokesman for the Helmand governor told the BBC that special forces had been deployed to the area.
Afghanistan's Chief Executive Abdullah Abdullah held an emergency meeting with security ministers and pledged "immediate action" against the Taliban.
The Taliban have also come close to overrunning the neighbouring district of Gereshk, according to local media reports. Gereshk is strategically placed on the country's main circular highway.
Earlier, the deputy governor of Helmand complained of a lack of government support in an open letter on Facebook to President Ashraf Ghani.
Mohammad Jan Rasoulyar warned that the province could fall to the Taliban.
He said at least 90 soldiers had been killed in the latest fighting and claimed Mr Ghani's entourage was not telling him the reality of the situation.
"Helmand will collapse to the enemies and it's not like Kunduz, where we could launch an operation from the airport to retake it. That is just impossible and a dream," he said.
Muhammad Kareem Atal, the head of Helmand's provincial council, said in quotes carried by AP that about "65% of Helmand is now under Taliban control... in every district either we are stepping back or we are handing territory over to Taliban".
In recent months, Taliban insurgents have launched multiple offensives, stretching the Afghan army, which is short of reinforcements, fuel and ammunition.