NOUAKCHOTT (AFP) - Al-Qaeda's north Africa affiliate has claimed the kidnapping of a Swiss woman in Mali in a video seen by AFP on Wednesday, with an English-accented militant listing conditions for the hostage's release.

Beatrice Stockly, who was previously abducted by Islamists in northern Mali's Timbuktu in 2012, was taken for the second time on Jan 7 by armed men who stormed her home in the country's fabled city.

The eight-minute video includes triumphant montages of militants brandishing weapons and a masked speaker with an English accent who claims responsibility for the abduction on behalf of Al-Qaeda in the Islamic Maghreb (AQIM).

"Beatrice Stockly is a Swiss nun who declared war against Islam in her attempt to Christianise Muslims," the speaker said.

A video released on YouTube in June showing two other Western hostages held by AQIM also featured a militant with an English accent.

The man in the new video appeared heavier than the man in the June video and their voices sounded different.

In the new message, the militant said Stockly was released after the first kidnap on condition that she would not "return to any Muslim land preaching Christianity.

"But she had nullified this agreement and returned to Timbuktu," he said in English.

Stockly has previously been identified as a missionary and social worker in her 40s who had lived in Timbuktu for years.

AQIM's use of an English-accented spokesman has parallels to "Jihadi John", the British extremist born Mohammed Emwazi who was identified as the executioner of Western hostages in a string of Islamic State in Iraq and Syria (ISIS) group videos before he was killed in a drone strike.

With at least three other fighters dimly lit in the background, the speaker listed conditions for Stockly's release.

They include freeing a number of AQIM fighters jailed in Mali and one of their leaders, Abu Tourab, detained at the International Criminal Court at The Hague.

Abu Ahmad Tourab is the nom de guerre of Ahmad al-Faki al-Mahdi, who is accused of ordering the destruction of historical monuments in Timbuktu in 2012.

Tourab, who was a leader of the Al-Qaeda-linked Malian group Ansar Dine, is the first militant to appear before the war crimes court.

Stockly appears at the end of the video dressed in a black hijab. She identifies herself and the date as Tuesday, Jan 19, 2016.

A Swiss foreign ministry spokesman told AFP that Bern was "aware of the video in question," and called for the hostage's unconditional release.

Northern Mali has remained restive since a loose coalition of Islamists and Tuareg rebels overran the region in 2012.

Islamic militant fighters were largely chased from the area in 2013 by a French-led military intervention, but entire swathes of the area remain beyond the reach of both the Malian army and foreign troops.

The speaker in the video said AQIM had developed an expertise in dealing with Western hostages and was prepared to be "patient" while waiting for its demands to be met.

Stockly's capture is believed to be the first in northern Mali since the kidnap and murder of two French journalists late November 2013 in Kidal.

But an elderly Australian doctor and his wife were seized by militants in a remote town in neighbouring Burkina Faso on the night of Jan 15-16.

That abduction, also reportedly carried out by fighters from AQIM, coincided with a militant assault on an upmarket hotel in Burkina Faso's capital Ouagadougou that left at least 30 people dead and raised fears of a widening Islamist threat in the region.

When Stockly was first abducted she was said to be the last Westerner living in Timbuktu, which she refused to leave when it fell to Ansar Dine.

Two weeks after her capture, special forces from Burkina Faso swept into rebel-held northern Mali aboard a helicopter and whisked her to safety in a pre-arranged handover.

At the time, around two dozen hostages were seized in the Sahel region, most of them held by AQIM and another Islamist group, the Movement for Unity and Jihad in West Africa (MUJAO).

Almost all were subsequently released.

Aside from Stockly and the Australian couple, three other hostages remain in captivity, a South African and a Swede seized in 2011 - who were shown in AQIM's June video - and a Romanian snatched in 2015.