More than 800 Taliban insurgents have launched a major offensive in southern Afghanistan to try to gain territory recently vacated by US troops.

Five days of fighting have so far left about 40 civilians dead.

"About 800 fighters started to storm four districts of Helmand last Thursday night," Helmand provincial governor spokesman Omar Zwak said.

"At least 21 Afghan forces have died and close to 40 civilians were killed."

The Taliban launched its summer offensive in the middle of May and has ramped up attacks across the country, a major concern for the government, as most foreign troops leave by the end of the year.

Helmand province is a major route for the transit of opium and some districts are controlled by drug dealers and the Taliban.
Attaullah Afghan, a tribal elder in Sangin, said the Taliban attacks aimed to try and open a route to the border to smuggle narcotics.
In a separate incident, two rockets landed in Kabul last night, one in the vicinity of the airport, wounding four people.