Armed gunmen attacked the bus and two cars in central Mozambique in the early morning on the main north-south highway, in the second assault this week since Renamo tore up a 1992-peace deal.
"This attack by Renamo once again resulted in the loss of a human life," said presidential spokesman Edson Macuacua in the central city of Beira.
"A minibus was set alight and 10 civilians injured, four of them seriously. Two of the injured were children," Macuacua said in comments sent to media. Other sources said three vehicles had been attacked.
The assailants were also accused of stealing the belongings of victims during the incident, which took place between the Save River and the town of Muxungue, where Renamo militants attacked a police station in April.
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"Armed men came out of the woods, opened fire and hit the driver in the forehead or the face," said Felisberta Moutinho, a survivor of the attack.
She also attributed the assault to Renamo, whose militants have been attacking civilian vehicles travelling along this stretch of the road over the past six months.
Since then vehicles have often travelled in military convoys, but today's group had risked the road without escort.
She said she ran into the woods with her two children until she spotted a group of police vehicles.
"A while later we heard explosions," she added.
Today's attack came a day after Renamo announced its leader's right-hand man and member of parliament Armindo Milaco had been killed by a howitzer in an assault on the group's base on Monday.
Milaco, a former child soldier, was head of national recruitment for the movement.
After losing their military headquarters to government troops, Renamo declared the two-decade peace deal over and accused the Frelimo-led government of killing multiparty democracy.