A spokesman for Nato, Major Toby Jackman, said four British soldiers were wounded by the blast on Monday, but their condition is unclear.
Afghan police reported that four Afghan civilians had been killed and four were wounded according to Jackman.
The explosion occurred at 10.15am on the road from Kabul to Jalalabad when a bomb exploded in a moving car.
Elsewhere on Monday, a Nato soldier was killed and several others wounded in a "friendly fire" in the southern province of Kandahar.
Nato said the accident occurred during an anti-Taliban operation in the Panjwayi district when ground troops requested air support.