Witnesses in southern Somalia say they heard huge explosions Thursday near the port town of Kismayo.

The witnesses say the blasts took place south of the city, which is controlled by the Islamist militant group al-Shabab.

It is not clear what caused the explosions. Witnesses told the French News Agency that they also heard the sound of aircraft.

The insurgent group al-Shabab is trying to topple the United Nations-backed government and turn Somalia into a strict Islamic state.

Al-Shabab rules much of southern and central Somalia, while the government controls only small parts of the capital.

However, government and African Union forces have retaken parts of Mogadishu in an offensive that began in February.

Somalia has not had a functioning central government since the fall of dictator Mohamed Siad Barre in 1991.