* Parliamentary election first of three votes
* President poll on April 9, state elections on April 16
* Campaigning in some areas marred by violence
LAGOS, April 2 Nigeria begins three successive weekends of nationwide elections with parliamentary polls on Saturday, a test of whether Africa's most populous country can break with a history of vote fraud and violence.
Ballot stuffing, intimidation of voters and thuggery were so widespread in the last elections in 2007 that foreign observers questioned whether they reflected the will of the people, saying they fell far below international standards.
The electoral commission hopes a new voters' register, tighter polling procedures and better security will help stamp out fraud, but there has already been violence in several regions during campaigning.
"Twelve years ago, our dear country returned to democratic rule and we began a journey that many expected by now would have produced a stable democratic system ... Unfortunately, this is still not the case," said Attahiru Jega, chairman of the Independent National Electoral Commission.
"The elections we are about to commence ... provide the chance for us as a nation to get it right."
Land borders were closed ahead of Saturday's vote and only election officials, security forces and emergency staff were allowed to travel on the roads during voting hours.
Gunmen threw explosives into a police station in the central city of Bauchi late on Friday in an apparent attempt to cause panic, although many officers had already left for the day and there was no immediate confirmation of casualties.
Police in Delta state in the oil-producing Niger Delta, where there has been political violence in the past, said they had arrested two men in a minibus carrying AK-47 rifles, ammunition and a rocket launcher days ahead of the vote. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Graphic on elections: link.reuters.com/xet78r For more stories, background and analysis: [nLDE68H051] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
The build-up to the polls has risked exposing ethnic and religious fault lines in the country of 150 million people, roughly split between a Muslim north and Christian south but with sizeable minorities living in both regions.
There have been isolated bomb attacks on campaign rallies, riots in the state of Akwa Ibom on the edge of the oil-producing Niger Delta, a series of killings in the remote northeast blamed on a radical Islamist sect, and sectarian clashes in the central "Middle Belt" in recent weeks.
In other areas, observers have seen less evidence of politicians arming gangs to intimidate and harass voters than in the run-up to the last polls in 2007.
Saturday's vote will be a litmus test for the presidential election a week later and the state governorship polls in two weeks' time, both of them ballots in which the stakes for the country as a whole are considerably higher.
In Nigeria's do-or-die political culture, parliamentary elections are also fiercely contested by candidates eager for the spoils of the job -- a pay package whose allowances alone top $1 million a year. [nLDE7300WJ]
Violence could reduce the turnout in the later polls.
President Goodluck Jonathan is seen as the front-runner in the presidential race on April 9, but the ruling People's Democratic Party (PDP) is expected to see its parliamentary majority reduced.
The PDP holds more than three-quarters of the 360 seats in the House of Representatives and of the 109 in the Senate.
The National Emergency Management Agency has cancelled leave for its staff and identified a third of the country's 36 states as potential flashpoints during the elections.
Amnesty International said at least 20 people had been killed in political attacks and clashes in the past two weeks, and scores of cars and buildings had been burned. (For more Reuters Africa coverage and to have your say on the top issues, visit: af.reuters.com/ ) (Additional reporting by Abdulwahab Muhammed in Bauchi, Austin Ekeinde in Port Harcourt, Camillus Eboh in Abuja; Writing by Nick Tattersall; Editing by Andrew Dobbie)
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