The United Nations said it was investigating reports of serious human rights abuses, including the execution of civilians, in northern Mali following clashes last week between northern Tuareg separatist rebels and pro-government militia.

UN-brokered peace efforts in Mali's north are in danger of unravelling because of repeated violations of a ceasefire between the Tuareg-led Coordination of Movements of Azawad (CMA) and the pro-government factions around the flashpoint northern town of Menaka. The clashes on Thursday killed at least six civilians, including a Malian aid worker, rebels and a local source said.