A probe into last month's hostage taking at a hotel in Mali's capital Bamako has been slowed by procedural differences between Malian investigators and their foreign counterparts, sources said Saturday.

The investigation into the November 20 attack on the Radisson Blu in Bamako which left 20 people dead is being carried out by Malian investigators as well as experts from the United Nations, France, Canada and Belgium.

A South African charity said Tuesday it had obtained fresh video footage of a South African and a Swede who were kidnapped in Mali four years ago and are being held by Al-Qaida.

Gift of the Givers, a disaster relief charity, earlier this year got involved in negotiations for the release of Stephen McGowan, a South African citizen and Johan Gustafsson, a Swedish national.

Armed men attacked a lorry carrying migrants in northern Mali, killing four people and wounding six, U.N. and medical sources told AFP on Monday.

Four men on motorbikes opened fire on the lorry as it traveled towards Kidal, in the country's far northeast, a medical source said, citing witness accounts.

Two U.N. peacekeepers and a civilian were killed and 14 others were injured in a rocket attack Saturday on a U.N. base in the northeastern Malian town of Kidal, U.N. and local sources said.

"Our camp in Kidal was attacked early this morning by terrorists using rockets," said an official from the U.N. peacekeeping mission in Mali (MINUSMA), adding that two Guinean U.N. peacekeepers and a civilian contractor were killed. A local official confirmed the report.

Germany will send up to 650 soldiers to Mali, Defense Minister Ursula von der Leyen said Wednesday, to provide some relief to France in its global fight against the Islamic State jihadists.

Von der Leyen made the announcement hours before German Chancellor Angela Merkel travels to Paris to meet President Francois Hollande to discuss support in the wake of the deadly November 13 attacks by the Islamic State group in the French capital.

A U.N. employee was killed Tuesday in an attack on a peacekeeping convoy in northern Mali, Secretary General Ban Ki-moon said.

The attackers used explosives on the road from Goundam to Timbuktu where the vehicles from the U.N. MINUSMA force were traveling, he said.

Mali began three days of national mourning Monday for the victims of a jihadist siege at a luxury hotel that left at least 19 dead, with neighboring Senegal, Mauritania and Guinea joining in solidarity.

"The investigation is advancing," said prosecutor Boubacar Sidiki Samake, who is in charge of the anti-terrorist probe.

Jihadist gunmen stormed a luxury hotel in Mali's capital Friday, firing automatic weapons and seizing more than 100 guests and staff in a hostage-taking that left at least 27 people dead.

Special forces staged a dramatic floor-by-floor rescue at the Radisson Blu hotel in Bamako, according to local television and security sources, to end the nine-hour siege.

Once bustling with sinewy young men like any other farming village in rural Mali, Kodjan is starting to look distinctly grey.

Little by little, the demographics of the settlement are altering as its youth join the exodus of African migrants looking for a better life in Europe.

Former Tuareg rebels in northern Mali and rival pro-government armed groups said they sealed a peace deal Thursday to end hostilities after days of talks.

Mali was hit by violence between the two sides in August and September despite a peace deal signed earlier this year.