Amnesty International on Tuesday called on authorities in Mali to investigate extrajudicial killings following the discovery last week of a mass grave containing six bodies.The rights group said it had collected evidence that "the six bodies found in a mass grave on 25 March had been arrested by the military three days earlier in the village of Dogo and taken away to an unknown location.""This macabre discovery comes after weeks of escalating violence which has left civilians in central Mali caught in the crossfire, facing enforced disappearances and unlawful killings by the military on one side, and roadside bombs and abductions by armed groups on the other," Amnesty's West Africa researcher Gaetan Mootoo said in a statement."We are urging the Malian authorities to investigate reports of enforced disappearances andKEEP UPDATED on the latest news from around the continent by subscribing to our FREE newsletter, Hello Africa.FOLLOW News24 Africa on Twitter and Facebook. extrajudicial killings of civilians in the central region, and bring all those suspected of criminal responsibility to justice," Mootoo said.The UN Mission in Mali (MINUSMA) on March 29 expressed "deep concern" over the increase in "serious violations and human rights abuses against civilians, including cases of summary execution" in the centre of the country, where jihadist groups are particularly active.MINUSMA, which has 12 000 peacekeepers in Mali, said it had recorded at least 85 major violent incidents and armed confrontations that resulted in at least 180 civilian victims, including 15 women and 17 children, since the beginning of the year.It said it was also worried about the extent of intercommunal violence in the central region, which has killed at least 50 people."Some cases are attributable to community self-defence groups," said MINUSMA, which welcomed Prime Minister Soumeylou Boubeye Maiga's recent visit to the restive region and the government's commitment to "shed light on serious violations and human rights abuses".Maiga, who is charged with improving Mali's security situation, vowed to disarm militias during visit to Koro on March 25.In early 2012 Islamist extremists linked to Al-Qaeda and other armed groups took control of Mali's desert north, but were largely driven out in a French-led military operation launched in January 2013.That insurgency has since spread to the country's centre, where local grievances are exploited by the Islamists in a region awash with guns.Another problem is deadly clashes between farmers and herders driven south to feed their animals in recent years.