African Union troops said Sunday they had launched a new offensive against Al-Qaeda-affiliated Shebab rebels in southern Somalia, vowing to flush the insurgents out of rural areas.

The African Union Mission in Somalia, or AMISOM, said "Operation Jubba Corridor" was launched on Friday in the Bay and Gedo regions south of the capital Mogadishu along with Somali government troops.

Officials and witnesses confirmed heavy fighting was raging near the Shebab strongholds of Dinsor and Bardhere, and said the militants hit back with a suicide car bomb attack against a convoy of Ethiopian troops, who are leading the offensive.

"The operation will ensure that all the remaining areas in Somalia will be liberated and peace restored," AMISOM said in a statement.

A Somali military official in the region, Mohamed Osman, confirmed heavy fighting between AMISOM and Somali troops on one side and the Shebab on the other.

"There are heavy clashes going on between our forces and Al-Shebab militia along the road that leads to Dinsor. The militants ambushed a military convoy," he said.

Witnesses who live close to the battleground said a suicide attacker struck the convoy with a car bomb loaded with explosives. There were no immediate reports on casualties.

The offensive was launched days after Kenyan government reports that a US drone strike in the region killed at least 30 Shebab rebels, among them several commanders.

It also comes several weeks after last month's Shebab assault on a AMISOM base which left dozens of Burundian soldiers dead in one of the single deadliest incidents since AMISOM soldiers arrived in Somalia eight years ago.

The Shebab, meaning "youth" in Arabic, emerged out of a bitter insurgency against Ethiopia, whose troops entered Somalia in a 2006 US-backed invasion to topple the Islamic Courts Union that was then controlling the capital Mogadishu.

Shebab rebels continue to stage frequent attacks, seeking to counter claims that they are close to defeat after losing territory in the face of repeated African Union and Somali government offensives, regular US drone strikes against their leaders and defections.

Currently affiliated to Al-Qaeda, there has been mounting speculation that the group could shift its allegiance to the Islamic State group.

In a message marking Muslim Eid celebrations on Friday, Shebab leader Ahmed Diriye -- also known as Ahmed Umar Abu Ubaidah -- outlined plans for the group to increase its operations outside of Somalia and particularly in Kenya.