HERAT (Reuters/AFP) - An Afghan police commander and 12 junior officers have defected to the Taliban after poisoning seven comrades, government officials in the western province of Farah said on Tuesday.

The commander, named only as Mirwais, was in charge of a checkpoint in the Bala Boluk district when he and his unit defected to the Taliban and handed over their equipment and weapons, including military vehicles. “He was a police commander for a checkpoint in Shewan village. He joined the Taliban with a Humvee, a Ranger, radios and 20 guns,” said Abdul Rahman Zwandai, a spokesman for the Farah governor.

The seven police were poisoned because they refused to join the rebellion, he said. All were taken to the Farah hospital and an investigation would be launched.

Farah, bordering Iran, is one of western Afghanistan’s most insecure provinces, although the west is relatively secure compared to insurgent strongholds in the east and south. The defection was the first time that police had joined the Taliban and taken so much equipment with them, Zwandai said, and will worry Western backers looking to hand security to Afghan forces by the end of 2014.

But national intelligence officials denied reports in some Afghan media that two members of the country’s High Peace Council, which leads government efforts to reconcile with the Taliban, had also defected to the insurgency. “I’m not sure anyone from the HPC would have joined the Taliban,” said National Directorate of Security deputy spokesman Shafiqullah Tahiri.

Meanwhile, gunmen believed to be Taliban insurgents have shot dead a US civilian and two of his Afghan colleagues in an area near Kabul which has seen a surge in militant violence in recent months, officials said.

The American was driving along the Ghorband valley in Parwan province, north of Kabul, when he was attacked and killed, Afghan officials and the US embassy said.

“We can confirm that a US citizen was killed in Parwan Province on Monday,” an embassy official told AFP. The spokesman said the victim was a civilian but refused to give further details.

A senior official in Parwan province told AFP the man was an electrical engineer who was travelling to a survey project for the rural development ministry. “He along with two Afghans were driving in a mini-van. Along the road they were chased by two or three insurgents for about half an hour. When they got to a certain area... they were shot at from the (chasing) car,” the official said on condition of anonymity.

Meanwhile, at least six Afghan children were killed on Tuesday after a bomb exploded in central Afghanistan’s impoverished Ghor province, officials said.

The children, aged between seven and 14, were grazing animals in Taywara district when they found the device partially buried under the mud, provincial spokesman Abdul Hai Khatibi told AFP. “As they pulled a wire attached to the weaponry, the explosion went off killing seven children,” Khatibi said.

Provincial Police Chief Delawar Shah Delawar said six children were killed while one was critically wounded. Delawar blamed the Taliban for planting the device, saying a group insurgents active in the district had attacked a nearby police checkpost two nights earlier.

“This is the Taliban’s work, they have repeatedly attacked police in this district recently. They fire rockets and use mines to target our police,” he said. Delawar added that security forces in the district were preparing to launch an operation to clear insurgents from the area. Improvised Explosive Devices (IEDs) planted on Afghan roads are a common insurgent tactic but they frequently miss their intended target - Afghan and Nato troops - resulting in civilian deaths.

According to the United Nations, the number of civilians killed in the war has risen steadily in the past five years, reaching a record 3,021 in 2011 - the vast majority caused by insurgents.

A recent UN report showed child casualties from Afghan conflicts rose by over a quarter last year with an average of nearly five children killed or injured every day in 2011.