Mogadishu (AFP) - At least 13 people were killed on Tuesday in twin bombings near UN and African Union buildings adjoining Mogadishu's airport, police said, in what the jihadist Shabaab group claimed as a suicide attack.

The Al-Qaeda aligned Shabaab group is blamed for a string of bloody assaults in Somalia and neighbouring Kenya, and is fighting to overthrow Mogadishu's internationally-backed government.

"At least 13 people were confirmed to have died in two explosions, one of the vehicles went off near a security checkpoint and another close to a UN compound," said Bishaar Abdi Gedi, a police official.

"The security forces have managed to intercept the attackers and foiled the attacks," Gedi said.

A Shabaab statement said it was a suicide attack by its militants.

"The two explosions were carried out by two brave Mujahedeen suicide bombers and they have targeted two different locations where the so-called AMISOM peacekeepers are stationed," it said, referring to the African Union mission to Somalia.

An AFP journalist at the scene heard gunfire after the explosions tore through the area.

- 'Looks like an attack' -

The city's airport is heavily fortified and adjoins the capital's main base for AMISOM, the 22,000-strong force backing the government in the battle against Shabaab insurgents.

AMISOM troops were deployed to Somalia in 2007 to defend the government against attacks by the Shabaab.

"Around 9am there was an explosion outside one of our gates, about 200 metres away," mission spokesman Joe Kibet told AFP.

"It looks like an attack, they intended to attack. Now the situation is calm and our personnel is working on it," he added.

The Shabaab were forced out of the capital five years ago but continue to carry out regular attacks on military, government and civilian targets.

In recent months they have claimed attacks on bases of the African Union peacekeeping mission in Somalia (AMISOM) as well as civilian targets including hotels.

This year is considered critical for the group, which is eager to disrupt an expected change of government leadership due in the coming months.

Somalia was supposed to hold national elections this year but is instead going to hold what diplomats call a "limited franchise election" in which ordinary citizens do not participate. The UN now hopes a one-person-one-vote election will be possible in 2020.