A hand grenade, thought to be a toy bomb, exploded in the hands of two children, killing them along with a woman and a man in Pakistan's southwestern Balochistan province Sunday, a local official said.

Three other children were injured, who were playing with the supposedly toy bomb, official Muhammad Naseer said.

The incident occurred in the town of Mashkeel, some 600 km from Quetta, the provincial capital.

Muhammad Naseer said that the children found the bomb in a jungle and brought it to home and were playing with it.

The bomb exploded with a big bang, killing mother, her two children and a young man.

A girl and two boys, who were playing there, were also injured.

Reports from Quetta said that such incidents have also taken place in Balochistan in the past.

Four people were killed when a toy bomb exploded in 2005 in Mastung, another major town in Balochistan.

Officials believe that some time drug smugglers also smuggle weapons. They hide weapons in deserts. Smugglers also keep on shifting the arms from one place to another when they find an opportunity.

The authorities have started a probe as to how the children found the bomb.