The runner-up in Nigeria's presidential poll, Gen Muhammadu Buhari, has said there were widespread irregularities in Saturday's election. The ex-military leader told US radio that there were areas in the south where his supporters were not allowed to vote. He said his party would challenge the result legally and urged to maintain calm after riots broke out in the north. His rival Goodluck Jonathan, a southerner, was declared winner in the presidential poll, with the electoral commission saying he received about 57 per cent of the vote. Gen Muhammadu Buhari said his Congress for Progressive Change party had noticed irregularities in the south and south-east of the country. However, according to International observers, the election was reasonably free and fair. Mr. Jonathan, a Christian from the oil-producing Niger Delta, was appointed to the presidency last year upon the death of incumbent Umaru Yar'Adua, whom he had served as vice-president.