The guards were killed Monday when the vehicle they were riding in hit a roadside mine in the Shindland district of Heart province, the Bakhtar news agency reported.
Three others in the vehicle were injured.
On Tuesday, two civilians were injured in a suicide attack on Heart-Islamqala highway in Shabbush village in the Ghoryan district of the same province, police said.
A car containing an explosive device exploded on the highway as a caravan of coalition forces was passing by, they said.
The suicide vehicle was destroyed. The attacker was not identified.
The injured civilians were in satisfactory condition, police said.