KANDAHAR: More than 800 Taleban insurgents have launched a major offensive in southern Afghanistan to try to gain territory recently vacated by US troops, officials said Wednesday, adding that 40 civilians have died in five days of fighting.

Around 100 Taleban fighters have been killed, according to the Interior Ministry, in clashes that erupted as Afghanistan wrestled with a political crisis over alleged fraud in the June 14 election to choose a successor to President Hamid Karzai.

The assault highlights the challenges facing Afghan security forces battling the Taleban as US-led NATO forces pull out.

Officials said that 800 militants were involved in attacks centerd on the Sangin district of Helmand province, a hotbed of opium production and the scene of intense fighting during the 13-year insurgency.

Mohammad Zaher Azimi, spokesman for the Defense Ministry, said the Taleban were exploiting the security forces’ reduced firepower.

“The main reason for the attack is that now we don’t have the aerial coverage that NATO would provide in the past,” Azimi told a local news channel.

“This has given the Taleban the chance to freely move in some areas and mobilize for big offensives... but even without the help of NATO, the security forces have beaten back this attack.”

The last US troops pulled out of Sangin only last month, handing over their remaining bases to Afghan soldiers and police who have now taken on full responsibility for fighting the militants.

“About 800 fighters started to storm four districts of Helmand last Thursday night,” Helmand provincial governor spokesman Omar Zwak told AFP.

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

Zwak said reinforcements had been sent to repel the attacks in Sangin, Nowzad, Kajaki and Musa Qala districts, where 2,000 families have fled the violence.