Cotabato City, Philippines  - Seven people were wounded Monday in a grenade explosion in the southern Philippines, a city police chief said.

The explosion occurred in the house of Kentia Sampulna, a suspected illegal drug trader, in Cotabato City, 960 kilometres south of Manila, Senior Superintendent Willie Dangane said.

Dangane said Sampulna had just arrived at his house when he heard a hard object thrown on the roof, followed by an explosion. Sampulna was not hurt.

Investigators were still determining whether the motive of the attack was a family grudge or related to the alleged involvement of Sampulna in the illegal drugs trade. (dpa)