The African Union force battling Somalia's Al-Qaeda-linked Shebab rebels said Tuesday it had conducted new air strikes against a rebel base in the south of the country, the second attack in three days.

A statement from Amisom said its planes were after "senior leadership and foreign Al-Shebab fighters" at a base near the town of Jilib in Somalia's Middle Juba region.

It also claimed 50 insurgents were killed in the attack, which "further debilitated Al-Shebab's capacity to wreak havoc and terrorise innocent Somali civilians."

A Shebab spokesman, however, told AFP that only farmland was hit and five civilians wounded.

"The claim of Amisom is baseless and pure propaganda," said the spokesman, Abdulaziz Abu Musab.

Witnesses in the area contacted by AFP said there were several civilians hurt, but had no information on any Shebab casualties.

"We heard very big explosions as military jets flew over the town. Two of the bombs landed near Faragurow village leaving four civilians wounded but we don't know about other casualties they may have caused," said a local resident, Moalim Hassan.

Idle Ahmed, another resident, said Shebab militant fighters riding on pick-up trucks were seen rushing to the scene and stopped ordinary civilians from approaching.

"The jets targeted a Shebab military base but we don't know their casualties," he said.

The airstrikes on the town of Jilib are understood to be part of the offensive by the 22,000-strong UN-backed African Union force, who in March launched a fresh bid to wrest remaining towns from the Al-Qaeda-linked Islamists.

The impoverished town is a key Shebab hub in southern Somalia's Middle Juba region, some 320 kilometres (200 miles) southwest of Mogadishu.

It was not immediately clear where the jets were from, but Kenya is part of the AU force and has used its jets to strike Shebab bases before.

Hardline Shebab insurgents once controlled most of southern and central Somalia.

After withdrawing from fixed positions in the capital Mogadishu nearly three years ago, they have lost most large towns to the AU and government soldiers. However, they still regularly launch guerrilla raids.