At least 21 civilians were killed and 25 others injured in South Sudan on Friday during an attack by gunmen on commercial vehicles, a local government official said Sunday.

Akech Dengdit, Jonglei State Information Minister told Xinhua by phone that two cars traveling from the capital Juba to the eastern town of Bor were separately attacked in the remote area of Gemeza, some 75 km from Juba.

"The gunmen stopped the cars at what used to be a checkpoint between Gemeza and Safari Sudan. 21 innocent people were shot dead and 25 injured," Dengdit said.

"We don't know the motive of these unfortunate killings but we are working with relevant authorities in the area to investigate these killings," he added.

Dengdit said among the dead were women and children.

Daniel Justine, police spokesman said he received reports about the killings but police are yet to verify the casualty figures.

Gun violence along major routes in war-torn South Sudan have increased since renewed fighting erupted between forces loyal to President Salva Kiir and his former deputy former Riek Machar in July 2016.

In March, at least 20 civilians, including seven aid workers were killed in the same road linking the capital to the eastern parts of the East African nation.