U.N. spokesman Leocadio Salmeron said an army sergeant shot the two election workers in the eastern town Fataki, a town on Congo's border with Uganda. It was not immediately clear what prompted the shooting, but Salmeron said the soldier appeared to be drunk. The soldier was arrested by police, he said.
The killings sparked rioting, and villagers in Fataki burned down 43 polling stations and the ballots stored within them, Salmeron said from the eastern town of Bunia.
The violence came as tallies were posted at polling stations across vast Congo and hundreds of U.N. pickups and minibuses swept around the capital collecting ballots from the runoff, which pits President Joseph Kabila against his vice president and former rebel leader Jean-Pierre Bemba.
Personal security forces of the two candidates fought for three days in August over results after the first round of voting in July.
On Sunday, at least one person died as protesters who suspected ballot tampering ransacked a dozen polling stations and clashed with security forces elsewhere in northern Congo. A rights group said blockades set up by money-extorting soldiers prevented thousands from voting in the east.
A dozen polling centers had been scheduled to reopen Monday to give voters another chance in the northern town of Bumba after Sunday's violence. But electoral commission head Apollinaire Malu-Malu said that vote had been delayed until Tuesday to give time for electoral materials and officials to arrive.
The country's four-year postwar transition climaxed with the runoff between a president and a rebel warlord — a contest many hope will bring stability to a region that has been ravaged by years of dictatorship and wars that pulled in more than half a dozen African nations.
Both candidates have pledged to accept the results and international observers said Sunday's polls closed with relatively few incidents.
Vote counting began late Sunday, with electoral workers tallying ballots by battery-powered lanterns and candlelight. Some stations posted their local results as early as 11 p.m. but overall results are not expected for several days.
The electoral commission has said it will issue provisional results by Nov. 19.
"The country has been destroyed by the dictatorship and war," said Xavier Kekeli, a 44-year-old French teacher working an electoral station in Kinshasa that stayed open late into the evening to accommodate those kept away by morning rainstorms. "Everything now comes from the foreigners — even the candles ... now it's time for the Congolese to take on our own destiny."
In Kinshasa, where problems collecting and counting millions of ballots in the first round left the final tally open to criticism, the U.N. has commandeered trucks and cars from its various agencies to pick up votes and bring them to one of 14 collection centers.
The postwar transition has been secured by the largest U.N. mission in the world, a 17,600-strong force backed up for the vote by 2,500 European Union troops in Congo and Gabon.
Congolese are eager to see their tumultuous country take its place among the continent's modern democracies. Until a constitutional referendum last year, most people here had never voted. Out of a population of more than 58 million, 25 million were registered to vote.
Kabila is favored to win a five-year term.
"We have an impossible choice to make. Bemba is a bandit and Kabila is not intelligent enough to govern Congo. But we have to make do and hope for the best," said Nelson Bagula, 25, a law student in the eastern town of Goma. "Our country is so rich, but our people are the poorest. We are voting with hope that this will change."
Kabila, credited by many here with launching the postwar transition process, captured 45 percent of the first round vote, compared with Bemba's 20 percent. During his term as interim president, Kabila has kept a low profile and rarely made public appearances. But he has convinced foreign governments he is capable of governing.
During the war, Bemba ruled a large chunk of northeastern Congo with support from neighboring Uganda. Bemba is credited with accepting the power-sharing agreement that ended the fighting. The Central African Republic this year issued an international arrest warrant for Bemba for alleged involvement in a rebellion there. The case is before the International Criminal Court.
Rich in cobalt, diamonds, copper, gold and coltan, Congo gained independence from Belgium in 1960 and was ruled for 32 years by Mobutu Sese Seko, a dictator who plundered the country's mineral wealth, pocketing billions and doing little to develop the giant nation. Joseph Kabila's father helped depose Mobutu, but was then assassinated, leaving his son in power.
The new president will have to establish a unified army and regain control over lawless borderlands in the east, thousands of miles from Kinshasa, where rebels and militiamen accused of raping and pillaging residents collect their own taxes.