ANTOINE ROLLAND A group of influential opposition politicians in the Central African Republic has called for an annulment of last Sunday's election, saying that a third of voters were unable to cast their ballot because of insecurity. Voting took place amid an offensive by armed groups in rural areas long beyond the reach of government control in the sparsely-populated country of 4.7 million people. In the build-up, the government relied on United Nations' peacekeepers to deliver election materials to the provinces by plane because roads were made unpassable by heavy rains or rebel checkpoints. Results are expected to trickle in…