Mogadishu, Somalia: Somalia's Shebab insurgents assassinated a lawmaker and his guards Saturday, the president said, hours after US President Barack Obama said the Al-Qaeda affiliated militants had been weakened.

Gunmen sprayed the car of MP Abdulahi Hussein Mohamud with gunfire as he travelled through a southern district of the capital Mogadishu, killing him, his two guards and the driver.

President Hassan Sheik Mohamud said he was devastated at the attack, the latest in a string of murders of Somalia's lawmakers.

The lawmaker was martyred while serving the nation, but such killings will not deter us from going forward, Mohamud told reporters late Saturday.

The Shebab said in a statement that their mujahedeen fighters targeted and killed a member of the parliament and his guards, adding that they will continue targeting lawmakers.

The Shebab have carried out repeated attacks including a campaign of suicide attacks and assassinations targeting government figures.

UN envoy to Somalia Nicholas Kay called the murders a despicable act.

Witnesses said the militants fled after the attack.

They opened fire on the car of the lawmaker and all of the passengers including him died, witness Abdirahman Mire said.

The Shebab is fighting to overthrow Somalia's Western-backed government which is propped up and protected by the 22,000-strong African Union force (AMISOM).

The attack came as Obama, on a visit to neighbouring Kenya, praised AMISOM's efforts, but said while the insurgents had been weakened, the overall security threat posed by the group remained.

We have been able to decrease their effective control within Somalia and have weakened those networks operating here in East Africa. That doesn't mean the problem is solved, Obama said.

We can degrade significantly the capacity of the terrorist organisations, but they can still do damage, he added.

Somali government troops backed by African Union forces last week launched Operation Jubba Corridor -- an offensive it said was aimed at flushing the insurgents out of rural areas in southern Somalia in an operation involving Ethiopian and Kenyan forces.

On Saturday, there were reports of helicopters -- believed to be from Ethiopia -- carrying out airstrikes targeting Shebab fighters in the southern Bay region.

Government officials said the attacks had killed several Shebab fighters, but residents said civilians had also been killed.