The UN Security Council voted unanimously on Tuesday to extend the presence of its peacekeeping force in Congo, its biggest and costliest peacekeeping effort, for another year. The force endured the deadliest single assault on a UN peacekeeping force in almost 25 years when a rebel attack late last year killed 15 troops, AP reported. Congo has gone through decades of ethnic clashes, rebellions and violence carried out by armed groups and militias trying to control gold and other resources. Tensions have also simmered over President Joseph Kabila’s stay in office, despite his mandate ending in 2016. Elections have repeatedly been postponed, and they are now set for December 23. The UN's $1.1 billion-a-year peacekeeping mission counts over 16,000 troops and 1,300 police.