HERAT, Afghanistan: At least five people were killed and 20 more wounded when two bombs exploded in quick succession in the western Afghan city of Herat on Friday, officials said.

The incident happened in the evening when a group of young men and children had gathered to play at a ground where the bombs were planted.

"Five people have been killed and 20 others have been wounded," Sabit Harwi, spokesman for the intelligence office in Herat, told AFP.

Harwi said the local police defused two other bombs found in the area.

He said the entire area had been demined recently to remove all unexploded ordnances left from the war and the bombs that exploded on Friday appeared to have been planted just before the group came to play.

Ibrahim Mohammadi, head of Herat's ambulance service, confirmed the toll and said the dead included a child.

Herat is the country's third-biggest city, close to the border with Iran, but had remained relatively peaceful for several weeks.

In January, a bomb attached to a fuel tank of a minibus killed seven people in an area inhabited by the minority Shiite community in the city.

Security in Afghanistan has vastly improved since a two-decade long insurgency by the Taliban ended with the hardline Islamist group's capture of the capital Kabul in August.

However, there have been attacks reported in the country, including some claimed by the regional chapter of the jihadist Islamic State group.

Meanwhile in a separate incident earlier on Friday, five children were killed when an unexploded mortar shell accidentally blew up in the southern province of Helmand, Mohammad Qasim Riaz, an official with the department of information and culture, told AFP.