KABUL, Afghanistan — The Taliban staged three attacks in southern Afghanistan on Saturday, killing at least 20 Afghan soldiers as a high-level NATO delegation was visiting the country to discuss the peace process.

The insurgents have been striking checkpoints and small outposts at night in the turbulent southern provinces of Farah and Helmand.

In one attack, the insurgents detonated explosives packed into an American-made Humvee that had been captured from the Afghan Army. And in another, they made off with a Humvee, replenishing their supply.

In the most lethal strike, insurgents overran a checkpoint in Farah Province around 3 a.m. Saturday. An Afghan Army spokesman said that 18 government soldiers were killed and two others wounded, and that a firefight with the attackers had continued even after reinforcements arrived.