Mogadishu:
Somalia's Al Qaeda linked Shebab insurgents claimed responsibility for the attack on a key United Nations compound in the capital Mogadishu today, the first major attack in recent years targeting the UN.
"Our commandos have attacked the UN compound... we set off an explosion and have entered the compound, where we are fighting with the infidel forces," a senior Shebab official told AFP.
An AFP reporter said a loud explosion had been heard followed by heavy gunfire from the complex - home to UN humanitarian agencies - but the insurgents' claims they had entered the compound could not be immediately verified.
Government-run Radio Mogadishu reported that gunfire could be heard inside the compound, and that the attack had started after a suicide bomber blew himself up at the gates of the complex.
However, a UN source in Nairobi said that "all staff are in a safe room" inside the compound.
The compound - including both residential and office areas - is a short distance from the airport zone, the base of the African Union troops, but is guarded by its own security officers.
Somalia's capital has been hit by a series of attacks including suicide and car bombers, mortar attacks and shootings, although in recent weeks the city has been relatively calm.
Islamist Shebab militants used to control most of the seaside capital until it abandoned fixed positions in August 2011, but the insurgents have since carried out a string of attacks against the UN-backed government.
The last major attack was in April, when the Shebab sent a nine-man suicide commando unit to blast its way into Mogadishu's main court complex, some blowing up their explosives vests while others sprayed gunfire in a rampage that killed 34.