Nearly 69 million Nigerians registered to vote in a tight presidential election casted their ballot on Saturday and Sunday amid some bomb attacks from Islamic militants in the Northern part of the country.

The election in Africa’s largest economy and the most populous nation on the continent is the biggest ever on the continent and the first  in nine lections since its independence in 1960, where an opposition candidate has a good chance to defeat a sitting president.

The vote, which pit the incumbent President Goodluck Jonathan against former military ruler Muhammadu Buhari, has been marred with violence during the campaigns and was postponed for six weeks from its initial election date of February 14.

The tight vote in the oil rich nation has divided Nigerians along ethnic, regional and religious lines. This has threatened to spill over into post election violence.

In a previous presidential contest between the two front runners in 2011 nearly 1,000 people were killed in post election violence after Jonathan won.

Reuters reported that the main opposition party the All Progressives Congress (APC) said it will not accept results from at least one Southern state, a Jonathan stronghold, on ground that it’s supporters were attacked and prevented from voting.

“Whatever trash will (be) announced as the result of today’s election is not acceptable to us … (it is) a sham and a charade,” the APC said in a statement.

In other Northern states Islamic militants Boko Haram, who last month declared allegiance to the ISIS,  killed at least a dozen people in bomb attacks on polling stations. The bombs killed three people in Yobe state and 11 in neighboring Gombe, including an opposition parliamentary candidate.

AP reported that in some three villages in Gombe gun-wielding militants, who have vowed to disrupt the elections in their bid to install Sharia laws in the country, chased voters  from polling stations.

In addition to the Islamic uprising, Nigeria is beset by militants demanding a better share of oil revenues who attack petroleum installations in the south and deadly land disputes across the middle of the country between semi-nomadic Muslim cattle herders and mainly Christian farmers.

Both foreign and local investors are nervously waiting for the election results expected later on Monday. Thousands of Nigerians and foreign workers left the country ahead of the vote amid fears that post-election violence could erupt this week.

Long queues were formed outside banks across major cities in the country as people sought to withdraw emergency money. Queues were also long at food stores and fuel stations as Nigerians stockpiled ahead of the election.

“I’m getting my cash out now because I don’t know what is going to happen. If it gets bad, you don’t want to be stuck with no cash,” euro news quoted businessman Wale Olatunji in Abuja saying.