Nigerian prosecutors have decided not to press charges against a 15-year-old girl detained after killing a man who had attempted to rape her.

Police said she stabbed the man, a friend of her father's, in March when she had gone to his house to do chores.

But state prosecutors in the commercial capital, Lagos, say there is no evidence to support a murder charge.

At the time of her arrest, there was an outcry on social media by people saying she had acted in self-defense.

The teenager has been freed at a time of public protests over a wave of rapes and the killing of women in Nigeria.

Thousands have recently signed a petition calling for an end to sexual violence.

Many Nigerians say the country's legal system makes it hard to convict suspected rapists and blames women when they are victims of sexual assault.

Magistrate Philip Ojo said, in response to advice from Lagos State's Director of Public Prosecutions, that the teenager should be freed from custody as the "ingredients required to prove the offense of murder against the suspect were not all present.

"Also clearly intended to kill or cause grievous bodily harm to the deceased cannot be established," he said on Wednesday.

After the 51-year-old man had been killed, the teenager was held at a correctional home for girls in Lagos.

Neither the girl nor her family has commented on the incident.

'Lockdown rapes'

On Wednesday, Nigeria's Minister of Women's Affairs Pauline Tallen spoke about the "alarming" spike in rape cases in the country that has happened during the lockdown imposed in some areas to limit the spread of coronavirus.

"There has been an outcry against rape epidemic because of the lockdown," she said, calling on security agencies to speed up investigations.

Rape cases had recently increased by a factor of three, noting that "women and children are locked down with their abusers", the minister said.

The results of a survey published by NOIPolls in July 2019 suggested that up to one in every three girls living in Nigeria could have experienced at least one form of sexual assault by the time they reach 25.

It is not uncommon for rape to go unreported - with some victims and their families, fearing stigmatisation, police extortion, and a lack of trust in the judicial process, choose not to report cases to the authorities.