An Islamist rebel administration in Somalia had a 13-year-old girl stoned to death for adultery after the child's father reported that three men had raped her.

Amnesty International said the al-Shabab militia, which controls the southern port city of Kismayo, arranged for a group of 50 men to stone Aisha Ibrahim Duhulow in front of a crowd of about 1,000 spectators. A lorryload of stones was brought to the stadium for the killing.

Amnesty said that Duhulow struggled with her captors and had to be forcibly carried into the stadium.

"At one point during the stoning, Amnesty International has been told by numerous eyewitnesses that nurses were instructed to check whether Aisha Ibrahim Duhulow was still alive when buried in the ground. They removed her from the ground, declared that she was, and she was replaced in the hole where she had been buried for the stoning to continue," the human rights group said.

"Inside the stadium, militia members opened fire when some of the witnesses to the killing attempted to save her life, and shot dead a boy who was a bystander."

Amnesty said witnesses originally reported that Duhulow was 23-years-old, based on her appearance. But the human rights group found out from her father that she was a child.

Duhulow's father told Amnesty that when they tried to report her rape to the militia, the child was accused of adultery and detained. None of the men Duhulow accused was arrested.

"This was not justice, nor was it an execution," said Amnesty's Somalia campaigner, David Copeman. "This child suffered an horrendous death at the behest of the armed opposition groups who currently control Kismayo.

"This killing is yet another human rights abuse committed by the combatants to the conflict in Somalia, and again demonstrates the importance of international action to investigate and document such abuses, through an international commission of inquiry."

Amnesty said al-Shabab had created a climate of fear in which government officials, journalists and human rights activists faced death threats and killing if they spoke against the militia.