A missile hit a beach on Saturday used as a base by al Qaeda linked insurgents who want to topple Somalia's Western-backed leaders, the government and residents said.

A government spokesman in the southern region of Juba, where the missile landed, confirmed the strike near the port of Kismayo, but said he did not know which of the countries fighting al Shabaab had launched the attack, or whether there had been casualties.

It has exploded on a beachside that al Shabaab uses. It is 12 km (7 miles) away from the town (Kismayo), but we don't know which nation has carried out the attack, Mohamed Farah said.

Residents living in the coastal town, considered a base for al Shabaab's operations during its near five-year insurgency, said they saw a bright light streaking overhead in the night sky late Saturday.

It was a very big explosion, Ali Bulle, a resident of Kismayo, told Reuters from the port town.

First we saw a big light from the sea, it flew over us and seconds after, we heard a huge explosion.

Kenya sent its troops across its border into Somalia in October to crush the Islamist militants and has warned of air strikes from its air force and ships patrolling the Indian Ocean coastline on rebel enclaves across central and southern Somalia.

Kenyan military officials were not immediately available to comment, neither were al Shabaab.

The United States has used drones in the past to target top officials of al Shabaab, which wants to overthrow Somalia's Western-backed government and impose its harsh interpretation of sharia, the Islamic moral and legal code.

A fleet of foreign battleships is also patrolling the strategic sea-lanes off Somalia where pirates prey on commercial vessels and private yachts for ransom.

Kismayo is important to al Shabaab because the town provides taxes to the militant group for its operations and is a gateway for goods reaching areas under their control as well as a hiding place for some ships hijacked by pirates.

(Writing by James Macharia; Editing by Alison Williams)