Sierra Leone will send 850 soldiers to an African Union peacekeeping mission in Somalia, a military official said Thursday. The official, Lt. Col. Ronnie Harleston, Sierra Leone’s military attaché to the United Nations, said the troops would deploy in the middle of next year. They will join approximately 9,000 peacekeepers from Uganda and Burundi, who are currently trying to secure the Somali capital, Mogadishu, from Islamist rebels. Djibouti plans to contribute 850 troops to the force this month. The force has a mandate for 12,000 peacekeepers, but African Union officials say they would need 20,000 to try to pacify the entire country, which has been in a state of civil unrest for roughly 20 years.