Taliban fighters on Friday intensified clashes with Afghan forces and targeted militias allied with the government, officials said, stretching their dominance of border towns and closing in on two provincial capitals as foreign forces leave.

At least 10 Afghan soldiers and a commander of armed members belonging to the Abdul Rashid Dostum militia group in the northern province of Jowzjan were killed.

"The Taliban launched violent attacks on the outskirts of (provincial capital) Sheberghan this week and during heavy clashes a pro-government militia forces' commander loyal to Dustom was killed," said Abdul Qader Malia, the deputy governor of Jowzjan province.

The Taliban, fighting to reimpose their rule after their 2001 ouster by US-led forces, have stepped up their campaign to defeat the US-backed government as foreign forces complete their withdrawal after 20 years of war.

Another provincial council member said nine of the 10 districts of Jowzjan were now controlled by the Taliban and the contest to control Sheberghan was under way.

In southern Helmand province, damage to civilian property aggravated the humanitarian crisis as shops caught fire in a week-long battle to control the capital of Lashkar Gah.

The United Nations this week said it was deeply concerned about the safety of tens of thousands of people trapped in the city.

"Violence has only escalated and there is no way to assess the damage in Lashkar Gah as both sides are locked in an intense ground battle... it is hard to even recover bodies by aid agencies," a senior Western security official said in Kabul.

The Lashkar Gah office of aid group Action Against Hunger was hit by a bomb during fighting in the area on Thursday.

"Civilians find themselves in between warring parties. They are being displaced from their homes and are often the first victims of the conflict," said Mike Bonke, Action Against Hunger's Country Director in Afghanistan.

"Humanitarian organisations like Action Against Hunger try their best to support people's needs, but we need safety guarantees from all parties to be able to operate," he said in a statement.