At least 12 people were killed on Sunday when two Kenyan jets bombed the southern Somali town of Jilib, residents and officials said, as the east African nation fights to rid Somalia of Islamist al Shabaab rebels.

Kenya moved its troops into Somalia in mid-October in pursuit of Somali insurgents it blames for a series of kidnappings on Kenyan soil and frequent assaults on its security forces in the border province of North Eastern.

Twelve civilians died including six children and 52 others were injured after Kenyan jets bombarded an IDP (internally displaced people) camp in the town, said Mohamud Ali Harbi, a local elder in Jilib, 120 km (74 miles) north of the port of Kismayu.

Emmanuel Chirchir, the Kenyan military spokesman, could not immediately confirm the raid when contacted by Reuters, saying they were waiting for an operational update from the ground.

The jets bombarded two places, an al Shabaab base and a nearby IDP camp, Hassan Abdiwahab, a resident in Jilib, told Reuters.

But al Shabaab said the five bombs dropped by the planes hit a bus stop, the IDP camp and an area just outside of the town.

A top official of the group, Sheikh Muktar Robow Abu Mansoor, on Thursday urged their followers to attack Kenya with huge blasts in retaliation for the campaign that is being carried out jointly with Somali government troops.

The call followed two grenade attacks in the capital Nairobi that killed one person and injured over 20 more on Monday. Unknown militants also carried out two attacks on vehicles in the remote northern Kenya.

Mohammud Farah, spokesman for the Ras Kamboni militia that is allied to the Somali Transitional Federal Government said they seized a four-by-four vehicle laden with explosives that was headed to Kenya.

Our forces in patrol found the car 8 km away from the town on its way to Kenya and we have discovered different types of explosive materials in the car, Farah told Reuters from Dhobley town, which is close to the border.

The vehicle was carrying 10 passengers, four of whom were identified as al Shabaab fighters, he added.

Kenya said on Saturday it was committed to withdrawal from Somalia once it is satisfied that it has stripped the al Qaeda-linked group's capacity to carry out attacks across the border.

Although the Kenyan chief of defence forces said his troops had chased al Shabaab from the whole of Gedo region, the two-week old campaign has been slowed considerably by heavy rains.

Chirchir said the intense rains had started to abate, allowing Kenyan forces to plan an offensive of Afmadow in Lower Juba region, where al Shabaab has been digging in after reinforcing with fighters from other areas.

Now that the rains have subsided, the taking of Afmadow is likely. It should be very soon, he said.

Two Ugandan soldiers were injured on Saturday when African Union troops came under an al Shabaab attack in Mogadishu.

Rwanda's President Paul Kagame, South Africa's President Jacob Zuma and Tanzania's Jakaya Kikwete expressed their support for Kenya's military action in Somalia, the Kenyan presidency said in a statement from Perth, Australia, where President Mwai Kibaki was attending the Commonwealth summit.

(Additional reporting by Feisal Omar; Writing by Duncan Miriri)