MALI'S interim government has denounced the execution by stoning of an unmarried couple by Islamic extremists in the north of the country, describing it as a "dark-age practice".

"The government learned with indignation and astonishment of the stoning to death of a couple in Aguelhok by the extremists occupying northern Mali," read a statement from the communication ministry on Tuesday.

"At the same time as it expresses its sympathy to the families of the victims, the government severely condemns this dark-age practice and assures that this act will not go unpunished."

The statement said the government "reiterates its determination to continue to do everything to rapidly free the occupied zones in the north of Mali".

The hardline Islamists on Sunday placed an unmarried couple in holes in the ground and stoned them to death in front of about 200 people, in the first reported sharia execution since they occupied the north about four months ago.

A local official said the couple had two children, the youngest of whom was six months old.

The small town of Aguelhok is controlled by the Islamist group Ansar Dine (Defenders of Faith) allied with al-Qaeda in the Islamic Maghreb (AQIM) which is also present in the Kidal region.

The extremists occupied the main cities of Timbuktu, Kidal and Gao in late March in the chaos following a coup in Bamako.