ABUJA, Nigeria - Boko Haram fighters attacked poll stations in northeast Nigeria and a governor demanded elections be canceled in an oil-rich southern state Sunday as the count started for a presidential election too close to call.

Two electoral workers were killed Saturday in Boko Haram's campaign to disrupt the elections, chairman Attahiru Jega of the Independent National Electoral Commission told reporters.

Voting continued in certain areas Sunday after technical glitches with new biometric card readers prevented some people from casting ballots on Saturday.

The high-stakes contest to govern Africa's richest and most populous nation has come down to a critically close contest between President Goodluck Jonathan, 57, a Christian from the south, and former military dictator Muhammadu Buhari, 72, from the predominantly Muslim north.

Results are expected by late Monday. If there is no clear winner, a runoff must be held.

Suspected Boko Haram extremists attacked polling stations and destroyed election material in two northeastern towns Sunday, then advanced on Bauchi city, according to fleeing residents.

Soldiers engaged them in heavy gunfire, and a jet fighter patrolled skies above the city, they said.

Police spokesman Haruna Muhammad said security forces had halted the convoy of 10 vehicles holding "unidentified gunmen" at Dindima village, six miles from Bauchi. But gunshots erupted before nightfall Sunday, and authorities declared a curfew.

U.N. Secretary-General Ban Ki-moon said voting had been "largely peaceful and orderly." On Sunday, supporters of Buhari, staged a protest in southern Rivers state, alleging that election officials there had colluded with the ruling party to rig the election. Jega, said he was "concerned" about the allegations.

The election was delayed by six weeks to make time for a multinational counteroffensive against Boko Haram insurgents. But it will be up to the next president to root out militants from their rural hideouts.

Crucial economic choices lie ahead, too, as the price of oil, which has for years buoyed the country's economy, falls, and Nigeria's institutions remain plagued by corruption. For now, both sides are adamant that their candidate won.

This article contains information from the Washington Post.