SECURITY forces in Central African Republic have repelled an attack by armed groups seeking to seize the capital Bangui, Prime Minister Firmin Ngrebada said. The assault represents a marked escalation in fighting with rebel groups that erupted around a disputed December 27 election. The groups attacked towns close to Bangui last month but did not reach the capital as intended. A Reuters witness in Bangui heard explosions and later saw helicopters circling over the city. "The attackers who came in large numbers to take Bangui have been vigorously pushed back," Ngrebada said in a post on Facebook, urging citizens to…