Witnesses in Somalia say a large explosion has hit near an area held by al-Shabab militants outside of Somalia's capital.

The witnesses said the blast happened Sunday near Afgoye, about 30 kilometers from Mogadishu. They described a light in the sky followed by a heavy explosion.

Kenya's military has threatened to carry out airstrikes on rebel areas in Somalia, but did not immediately comment on the blast.

A spokesman for the military said a clash between Kenyan soldiers and al-Shabab militants in southern Somalia late Saturday killed nine rebels and wounded four soldiers. The spokesman said the military also seized weapons from the militants, including rocket-propelled grenades.

Kenya recently launched its military operation in what it deemed an act of self-defense, following several cross-border attacks blamed on Somali militants.

The military says hundreds of al-Qaida-linked al-Shabab fighters have been killed or wounded since the military incursion began.