A munitions explosion killed seven people and injured a child in South Sudan's Unity state, the aid group Doctors Without Borders said Tuesday.

The stockpile of unexploded ordnance, leftover from clashes between government forces and rebels last year, was stored in a container in the opposition-held Thar Jath, an oil-producing area.

The container blew up last week on Thursday, probably after locals set fire to the grass nearby to clear land for farming, said Doctors Without Borders.

All seven people killed were men and a 14-year-old old boy was left with wounds all over his body, said the organization.

South Sudan has been at war since December 2013 as forces loyal to President Salva Kiir try to put down a rebellion led by his former deputy, Riek Machar.

Despite international pressure for a political solution to the current conflict, South Sudan's warring factions have failed to reach a lasting peace agreement amid disagreements over how to share power and other issues.

Land mines and explosive remnants of war are present in all of South Sudan's states after decades of fighting, according to the U.N.

Doctors Without Borders warned there could be more unexploded munitions in Thar Jath from last year's clashes.