Twelve policemen have been killed in an "insider attack" in the southern Afghan province of Helmand, officials say.

A police source told the BBC that an infiltrator from the Taliban had allowed militants into the outpost in the regional capital, Lashkar Gah. The infiltrator fled with the Taliban.

Other reports said the infiltrator killed the policemen himself.

A spokesperson for the provincial governor confirmed the attack, but did not provide details.

Local television news reported that the Taliban seized weapons and ammunition from the scene, and that a local hospital had confirmed receipt of at least 11 bodies.

But a Helmand police official made no mention of a Taliban infiltrator in his comments on the attack.

"The Taliban attacked a guard with silenced guns and then entered the check post," Helmand deputy police chief Haji Gulai told Reuters news agency.

"They attacked other policemen with hand grenades and killed all of them. They later took their weapons and ammunition and escaped."

A Taliban spokesman later said the group carried out the attack and that 12 police had been killed.

Lashkar Gah has come under increased pressure from the Taliban in recent months.

The city of 200,000 people is seen as strategically important, and the key to holding Helmand province.

The province is both a fertile farming region and a centre for opium production, bordering Pakistan on one end and covering major routes between cities.

Thousands of people fled the rural areas to shelter in Lashkar Gah last August, before the city itself came under attack in October.

The city was previously the scene of heavy fighting between the Taliban and Nato-led forces before their withdrawal in 2014.