Three UN peacekeepers from Guinea have been killed in a mortar attack on their base in Kidal in northern Mali.
Thirty others were injured in the raid, which involved rockets and a truck bomb.
A local militia that signed a peace deal with the government last year blamed Islamist militants for the attack, Reuters news agency reports.
The UN is trying to restore peace to the north, which was overrun in 2012 by jihadists and ethnic Tuareg groups.
The al-Qaeda-linked insurgents, who fell out with Tuareg separatists, were ousted from northern towns by a French led-force in 2013.
Last June, Tuareg-led rebels and other Arab groups seeking more autonomy for the north signed a ceasefire agreement with the government.
The attack in Kidal comes 48 hours after the UN representative in the country, Mahamat Saleh Annadif, visited the area.
It is the latest in a series of attacks on the UN force, made up of 10,000 soldiers from dozens of different contributor countries – the majority from Mali’s West African neighbours.
“This serious act reflects the disarray of the enemies of peace since it comes at a time when the implementation of the peace agreement increasingly becomes a reality in Mali,” Mr Annadif said in a statement.
In a separate incident, three Malian soldiers were killed in an ambush on a military convoy near Timbuktu. It is not clear who is behind the attack.
Militancy in Mali
- October 2011: Ethnic Tuaregs launch rebellion after returning with arms from Libya
- March 2012: Army coup over government’s handling of rebellion, a month later Tuareg and al-Qaeda-linked fighters seize control of north
- June 2012: Islamist groups capture Timbuktu, Kidal and Gao from Tuaregs, start to destroy Muslim shrines and manuscripts and impose Sharia
- January 2013: Islamist fighters capture a central town, raising fears they could reach Bamako. Mali requests French help
- July 2013: UN force, now totalling about 12,000, takes over responsibility for securing the north after Islamists routed from towns
- July 2014: France launches an operation in the Sahel to stem jihadist groups
- Attacks continue in northern desert area, blamed on Tuareg and Islamist groups
- June 2015: Tuareg and northern Arab groups sign peace deal
- 2015: Terror attacks in the capital, Bamako, and central Mali