By Dan Isaacs BBC, Lagos

Amid growing controversy in Nigeria over the implementation of Islamic or Sharia law another two people have been sentenced to death by stoning.

A court in the north central state of Niger has convicted a man and a woman of adultery after they admitted to a relationship outside marriage.

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This the latest in a series of similar stoning sentences that have been strongly condemned by human rights groups both within and outside Nigeria.

None of the stoning sentences have so far been carried out.

Appeal backfires

Fatima Usman and Ahmadu Ibrahim are the latest names to be added to the growing list of Nigerian Muslims facing the punishment of stoning.

An Islamic court in Niger state passed the sentences after the couple confessed to a relationship outside marriage, which led to Fatima becoming pregnant.

Women's rights groups say Sharia is harsh for women

At the time she was still married to another man, although that marriage has since been dissolved.

Ironically, the couple had originally received only jail sentences but had appealed against what they considered then to be harsh judgements.

A higher Islamic court then ruled the death sentence and not a prison term was the mandatory punishment.

Unconstitutional

Earlier this month another woman, Amina Lawal, lost an appeal against her conviction for adultery and faces stoning, unless she can get the ruling overturned in the high court. She launched a high court appeal on Wednesday.

A man, Ado Baranda, sentenced to the same punishment, this time for the rape of a young girl, has chosen not to appeal.

His sentence may well be carried out very soon.

These Islamic punishments only apply to Muslims living in the countries majority Muslim northern states where the criminal code has been amended over the last two years to include the strict punishments of stoning, amputation for theft, and flogging for lesser crimes such as the drinking of alcohol.

Nigeria's federal government has declared the introduction of these laws by the northern states as unconstitutional but has done little to directly challenge them or overturn them.

Human rights groups at home and abroad have condemned the punishment, with Turkey becoming the latest foreign government to urge the Nigerian government to intervene on Miss Lawal's behalf.

Beauty queens due in Nigeria in November are threatening to boycott the Miss World contest in protest at Miss Lawal's sentence.

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