Mogadishu - (AFP) - At least six civilians were killed Sunday in an attack launched by the Somali youth movement near the municipality building in the center of the capital, Mogadishu, according to police.

Somali police spokesman Sadiq Dudisheh said at the end of the four-hour attack that a suicide bomber detonated a bomb that destroyed a building near the municipality complex, and an exchange of gunfire ensued.

"The six attackers were killed, five of them during an exchange of fire with the security forces, and one of them blew himself up," Dudisheh told reporters.

"Six civilians were also killed during the attack and the situation has returned to normal," he added.

The police said that all workers in the municipality building were rescued.

Eyewitnesses said earlier that the explosion damaged nearby buildings, and gunfire could still be heard near the municipality building.

"There is shooting inside the vicinity of the main building, but we do not know what is happening inside," said a witness who runs a shop near the headquarters.

"There were some casualties, but the whole area is cordoned off, and the security forces asked us to move away" from the site, he added.

Omar Nour, another witness, said he was inside the mall when the explosion occurred and "was lucky that he managed to escape unharmed."

The Al-Qaeda-linked Al-Shabaab extremist movement claimed responsibility for the attack on its social media pages, saying its fighters "made their way into the targeted building after killing the security guards."

Since 2007, the extremist Al-Shabaab movement has been fighting the federal government backed by the international community, and carrying out attacks in Somalia and neighboring countries.

The attack comes after the killing of seven soldiers on Friday in an army camp in the city of Galgad in central Somalia, about 375 km north of the capital, Mogadishu.

The US military said on Saturday that the attack - which took place in a Somali town that the army recaptured this week - involved more than 100 al-Shabab militants.

And the US military command for Africa (AFRICOM) stated in a statement that "the joint operations carried out by the partner forces on the ground and the collective strike in self-defense resulted in the destruction of three vehicles and the killing of approximately thirty terrorists from Al-Shabaab."

In recent months, the army and local tribal fighters have retaken swathes of territory in the center of the country in an operation backed by US air strikes and an African Union force.

However, Al-Shabaab fighters are still launching bloody attacks in retaliation, which shows that they are still able to strike in the heart of cities and target Somali military installations.

On Tuesday, Al-Shabaab launched a bloody attack on a military base in another part of central Somalia, the day after the government announced a "historic victory" over the jihadists.

Police said last week that eight people were killed in a roadside bomb blast in central Somalia claimed by al Shabaab. Earlier this month, 19 people were killed in two car bombings in the town of Mahas in the Hiran district of Hirshabelle.

Despite being pushed out of Mogadishu and other major cities more than a decade ago, Al-Shabaab is still active in parts of rural areas in central and southern Somalia.

In the jihadist group's deadliest attack since last year, 121 people were killed when two car bombs targeted the Ministry of Education in Mogadishu in October.

The group has also recently been active across the border in eastern Kenya participating in the African Union force in Somalia, where it has carried out several deadly small-scale attacks.