The soldiers were attacked with a remotely controlled bomb in the eastern Paktia province as they traveled toward their base, said Din Mohammad Darwish, the spokesman for the provincial governor.
The two wounded soldiers were in critical condition, Darwish said.
Separately, a blast ripped through a civilian car and killed four civilians south of the country's capital, Kabul, police said.
The force of the explosion hurled the front axle and wheels of the car to one side of the road and the rear axle to the other side.
The attack involving the civilians took place in the Musayi district of Kabul province, where a bomb had been freshly planted in the muddy, unpaved road, said regional police commander Gen. Zalmai Oryakhail.
Three men were killed in the blast and a fourth died on the way to the hospital, Oryakhail said.
He said it was not clear why the men were targeted, or if the bomb had detonated by a timer, remote control or the impact of the car on the device.
Militants often plant roadside bombs, usually targeting Afghan or international security forces. There are also many civilian casualties in the same types of attacks, however.
More than 6,000 people - a record number - have died this year in insurgency-related violence in Afghanistan, according to figures from Afghan and Western officials. Most of those reported killed have been militants.