An employee with the World Health Organization was among those killed in the weekend siege of a beachside hotel in Somalia's capital Mogadishu, the head of the UN health agency said on Sunday.

The siege left six civilians dead and another 10 wounded, according to police.

"I'm heartbroken that we have lost a WHO staff member in the recent attack in #Mogadishu, #Somalia," Tedros Adhanom Ghebreyesus, WHO director general, tweeted on Sunday.

"My heartfelt condolences to their families and to everyone who lost a loved one," he said. "We condemn all attacks on civilians and humanitarian workers."

The Al-Qaeda-linked Al-Shabaab have been waging an insurgency against the internationally backed federal government in Somalia for more than 15 years and have often targeted hotels, which tend to host high-ranking Somali and foreign officials.

The latest assault, for which Al-Shabaab claimed responsibility, began just before 8:00 pm on Friday (1700 GMT) when seven attackers stormed the Pearl Beach hotel, a popular spot at Lido Beach along Mogadishu's coastline.

It ended at around 2:00 am, police said, after a fierce gunfight between security forces and the militants, all of whom were killed during the battle.

The attack at Lido beach underscored the endemic security problems in the Horn of Africa country as it struggles to emerge from decades of conflict and natural disasters.

Al-Shabaab, which was driven out of Somalia's main towns and cities by an African Union force, still controls large swathes of countryside and continues to carry out attacks against security and civilian targets, including in the capital.