Veteran jihadist Mokhtar Belmokhtar speaks in this undated still image taken from a video released by Sahara Media on January 21, 2013. REUTERS/Sahara Media via Reuters TV

BAMAKO (Reuters) - Mali’s chief prosecutor said on Saturday that it has evidence that jihadist group Al Mourabitoun, led by veteran leader veteran militant leader Mokhtar Belmokhtar, was behind a November attack on a luxury hotel that killed 20 people.

Two Islamist militants stormed the Radisson Blu Hotel in Mali’s capital Bamako on November 20, killing six Russians, three Chinese and an American among others, in their bloodiest strike in the West African country in years.

Boubacar Sidiki Samake said that a scrap of paper with an Arabic inscription was found on the bodies of the two men, later killed by Malian Special Forces. The note sought the release of two prisoners who are members of Al Mourabitoun held in neighboring Niger and Mauritania, he added.

“These factors lead us to think that effectively Al Mourabitoun was at the origin of this attack,” Samake said on Malian state television late on Saturday.

Details of Mali’s investigation have been slow to emerge and until now the prosecutor has not said which of three jihadist groups to have claimed the attack was the most likely author and security experts disagree.

Al Mourabitoun together with close ally Al Qaeda in the Islamic Maghreb (AQIM) jointly claimed it as did Mali’s Massina Liberation Front.

Sahara-based Al Mourabitoun is led by Algerian Islamist leader Belmokhtar with a long history of leading insurgencies across north Africa and the Sahara. Libya said last year that he was killed in a U.S. air strike, although fighters have repeatedly denied this.

In the latest sign of worsening violence in Mali, gunmen abducted a Swiss missionary from her home in Timbuktu this week nearly four years after she was taken hostage as militants seized major urban centers with the help of Tuareg rebels.

French troops pushed them back into the desert in 2013 where they continue to pursue the militants.