KABUL — In an attack using a tactic long feared by Afghan officials, Taliban suicide bombers riding in two Afghan army Humvees clashed with security forces Saturday in southern Helmand province, killing six security personnel at a checkpoint, Afghan officials said.

The Afghan military and government officials have warned that insurgents could gain new advantages by turning military equipment against Afghan security forces.

As insurgents grabbed territory once controlled by Afghan forces in the past year, they also took weapons and Humvees provided by the US military from bases and checkpoints abandoned by Afghan forces, who are stretched thin fighting on their own without the combat assistance of NATO forces.

The exact number of Humvees taken by the Taliban is not clear, but accounts from multiple officials and Taliban commanders from across the country suggest that it could be more than 150.

The clash on Saturday unfolded in Sangin district, which has been on the verge of falling to the Taliban, prompting a major operation to push them back.

General Abdul Rahman Sarjang, the Helmand provincial police chief, said six Taliban suicide bombers riding in Humvees had been trying to carry out a “complex attack’’ on a nearby Afghan police and army base when they approached a checkpoint outside the base. A firefight erupted and two of the bombers managed to detonate their explosives, killing four police officers and two soldiers and wounding eight others. All of the insurgents were killed.

“Taliban are now using confiscated Humvees against us, and this is a matter of worry for us,’’ Sarjang said. “We are trying to destroy the seized Humvees. We are trying to target them and have targeted some of them already.’’

Local Afghan officials in recent months have been pleading with the central government and US officials for airstrikes to destroy the confiscated equipment.