KABUL, Afghanistan (CNN) -- A police commander and 13 junior officers in western Afghanistan have joined the Taliban in a move that is new and troubling for the struggling nation as international forces prepare to depart.

The commander, known only as Mirwais, had been with the Afghan National Police for a year and was in charge of two police stations and 20 officers in the Bala Boluk district of western Farah province, bordering Iran, said Abdul Rahman Zhewandai, a spokesman for the provincial governor.

He said the seven officers who refused to defect with Mirwais were found poisoned but they all survived.

Mirwais absconded with two police vehicles and 20 light and heavy machine guns -- including AK-47 rifles -- and rocket-propelled grenades, Zhewandai said.

Farah province is one of the most insecure areas of western Afghanistan, which is relatively calm compared to other regions. Zhewandai said the police defections were a first.

Mirwais belonged to the Taliban when the militants controlled Afghanistan between 1996 and 2001, when a U.S. invasion ousted them from power, Zhewandai said.

The defection comes at a time when the United States and its NATO allies are trying to prop up Afghan forces to take over the nation's security.

There have been several incidents of Afghans turning their guns on their international counterparts, including one Sunday when an Afghan policeman opened fire at a training center in western Afghanistan. Three Americans, most likely trainers at the West Zone Police Training Center in Herat province, were killed, along with the shooter.

Violence has also been on an uptick in strategically located Farah province, where the Taliban has been active.

In May, suicide attackers with explosives stormed the governor's compound, killing themselves and seven people.

In April, a Taliban attack in the province killed eight policemen.