HERAT: Suspected Taliban gunmen stopped two vehicles in central Afghanistan and shot dead 15 passengers at the side of the road, officials said Friday, in the latest attack to highlight the growing civilian toll from violence.

Only one man escaped the execution-style killing in Ghor province when the armed attackers gunned down 11 men, three women and one child.

“They ordered all passengers to stand in one line, and then they shot them dead one by one,” Abdul Hai Khatibi, spokesman for the governor of Ghor province, told AFP.

“One man managed to flee. All of the others were shot in the head and chest." Fahim Qaiem, Ghor provincial police chief, confirmed the incident and blamed suspected Taliban militants for the killings late on Thursday night.

There was no immediate claim of responsibility, and the Taliban often deny links to incidents where civilians are the victims.

The attack occurred the same day that two Finnish female aid workers were shot dead by unidentified gunmen while in a taxi in the western city of Herat.

A suicide bomber on a explosive-packed motorcycle in Takhar province also killed six civilians and wounded more than 20 in a crowded market as shoppers bought supplies for the upcoming festival of Eidul Fitr.

According to recent UN figures, civilian casualties soared by 24 per cent in the first half of 2014, while the International Crisis Group has said the “overall trend (in Afghanistan) is one of escalating violence and insurgent attacks."

Fears grow as Nato troop exit

Afghanistan is also mired in a bitter election dispute between presidential rivals Ashraf Ghani and Abdullah Abdullah that threatens to fuel instability and revive ethnic tensions that ravaged the country during the 1992-1996 civil war.

The political deadlock and soaring civilian casualties have caused deep disquiet among Afghanistan's international backers, who sent tens of thousands of Nato-led soldiers and billions of dollars in aid to the country.

Nato combat troops will withdraw from the country by December, winding down a 13-year war against the Taliban that has failed to defeat the Islamist group that ruled Kabul before being ousted in 2001.

The UN mission recently revealed that in the first six months of this year it had documented 4,853 civilians killed or injured, up 24 percent on the same period in 2013.

“The impact on civilians, including the most vulnerable Afghans, is proving to be devastating,” the UN report said.

At least 42 people were killed on July 15 in a devastating suicide bombing at a market of the southeastern province of Paktika, one of the deadliest attacks in the war-torn country in recent years.

Taliban insurgents oppose the ongoing election process, which is struggling to undertake an audit of all eight million votes due to a dispute between the two contenders over fraud allegations.

Some 23,000 ballot boxes are being transported by the Afghan army and Nato forces to Kabul to be examined and verified.

Abdullah led Ghani after the first round of vote to succeed President Hamid Karzai but preliminary results of the run-off, announced on July 7, showed Ghani ahead by over one million votes.

Abdullah rejected the result, saying that most of his opponent's ballots were fraudulent.

Abdullah draws his support from Tajiks and other northern Afghan groups, while Ghani is backed by Pashtun tribes of the south and east.

The recount has already sparked fresh arguments and fallen behind schedule.

The inauguration of Karzai's successor was due on August 2, but has now been delayed.