At least five people have been killed in an attack by the Taliban on a NATO convoy in Farah province in western Afghanistan.

A convoy of tankers carrying fuel to the US-led forces came under attack in Dizak village in the town of Bala Boluk in Farah province Monday night. During the incident, five Afghan security guards belonging to a private security firm were killed, according to Afghan authorities Press TV reported.

The assailants fled the scene following the attack. The Afghan Taliban have not commented on the incident yet.

Security forces have launched an investigation into the incident.

Private security firms in western Afghanistan are tasked with escorting NATO fuel tankers in the country.

Afghan President Hamid Karzai earlier ordered the Interior Ministry to intensify efforts to shut down domestic and foreign private security firms in the country.

Violence has also spread from Afghanistan's volatile south to relatively peaceful areas over the course of the past year, despite the presence of tens of thousands of US-led troops in the country.