Parliamentary elections in Nigeria have been postponed until Monday because of organisational problems, officials say. The electoral officials - who have apologised for the delay - say ballot papers have not been delivered in time to many polling stations. The decision is seen as a big blow to the credibility of the electoral body in Africa's most populous country. Some 73m people have registered for the parliamentary, presidential and gubernatorial polls over two weeks. Security has been high, with borders closed and only election officials, security forces and emergency personnel allowed to drive on roads during voting. Earlier, politicians were urged to put a stop to campaign violence. Amnesty International said at least 20 people had been killed in related attacks and clashes over the last two weeks. A bomb was thrown into a police station in the city of Bauchi on Friday in an apparent attempt to cause panic. No casualties were reported. Police in the Niger Delta also said they had arrested two men driving a minibus filled with assault rifles, ammunition and a rocket launcher. 'Emergency' "In order to maintain the integrity of the elections and retain effective overall control of the process, the commission has taken the very difficult but necessary decision to postpone the national assembly elections to Monday," Independent National Electoral Commission (Inec) head Attahiru Jega said on Saturday. "It is an emergency," he added. It is understood that aircraft were supposed to be flying in ballot papers and accreditation details from overseas but those planes were diverted away from Nigerian airspace, the BBC's Caroline Duffield in Lagos reports. There were angry scenes in polling stations across the country as word began spreading that the elections were postponed, our correspondent says. She adds that the move raises fears among some that Mr Jega's grip on his staff at the election commission is not tight enough, and people will wonder whether the coming elections over the next two weeks will run smoothly. The voting process had already started with large turnouts reported in cities such as Lagos and Kano before the announcement by Mr Jega. The elections will be the third nationwide polls in Nigeria since military rule ended in 1999. The previous votes - in 2003 and 2007 - were marred by allegations of widespread ballot stuffing, voter intimidation and violence. Security forces were also accused of siding with the People's Democratic Party (PDP), which has dominated politics since the return to civilian rule. Mr Jega earlier told the BBC that if Nigerians wanted to peacefully defend their votes at the polling stations, that was their right. And he threatened sanctions against any political leader engaging in violence or vote-rigging, even warning he would resign if necessary. In the election, 360 seats in the lower house of parliament, the House of Representatives, and 109 in the upper house, the Senate, will be contested. The PDP holds more than three quarters of the seats in both houses. Source: BBC