A 13-year-old girl stoned to death on accusations of adultery had apparently been raped, according to the UN.

The girl was put in a hole and stoned in Kismayu on October 28, in the first public killing by Islamic militants for about two years.

Local leaders claimed she was guilty under sharia law, while witnesses said they thought the victim was a 23-year-old woman.

In a statement, Unicef said: "Reports indicate that she had been raped by three men while travelling on foot to visit her grandmother in the war-torn capital Mogadishu.

"Following the assault, she sought protection from the authorities, who then accused her of adultery and sentenced her to death. The child was victimised twice - first by the perpetrators of the rape and then by those responsible for administering justice."

Unicef said the incident showed the vulnerability of girls and women in Somalia, which has suffered civil conflict for the last 17 years. In the latest cycle, Islamist rebels are fighting the government and their Ethiopian military backers.

A Human rights group identified the girl as Aisha Ibrahim Duhulow and said she was killed by 50 men who stoned her to death in a stadium in Kismayu, in front of around 1,000 spectators.

Her father and other sources said that she had been raped by three men.

When the family attempted to report the rape to the al-Shabab militia who control Kismayu, she was accused of adultery and was detained. None of the men she accused of rape were arrested.