Lagos, Nigeria ? Olusegun Obasanjo won an overwhelming victory in Nigeria’s presidential election, officials announced Tuesday, as opposition groups protested the balloting as rigged and threatened mass demonstrations.

Obasanjo won 62 percent of the more than 42 million votes cast in the weekend polling, election commission chairman Abel Guobadia said late Tuesday night. Obasanjo leading rival, former junta leader Muhammadu Buhari, was far back with 32 percent. More than 2.5 million votes were declared invalid.

“Having satisfied the requirements of the law and scored the highest number of voters, Chief Olusegun Obasanjo is hereby declared the winner,” Guobadia said.

The vote, marred by sporadic violence, was considered an important test of stability and democracy in Africa’s most populous nation. International monitors have expressed concern about fraud, including ballot-box stuffing and bribery.

The U.S. State Department said that widespread claims of electoral misconduct appeared to be credible. “We urge all parties with complaints of electoral malfeasance to present their evidence to the competent tribunals and for the tribunals the consider those complaints in a fair and transparent manner,” spokesman Richard Boucher said.

Threats of mayhem

Tensions were running high in a country frequently riven by bloodletting after opposition officials protested the outcome. Opposition groups earlier threatened to hold mass street protests.

Don Etiebet, chairman of Buhari’s party, stormed into the election commission headquarters shortly before the winner was announced, saying his party was refusing to endorse the results. He warned Tuesday that opposition supporters “will act appropriately according to human nature.”

“We do not need to tell the people what to do. They will know what to do when their mandate has been trampled upon,” he said, without elaborating.

Since an April 12 legislative vote, at least 35 people have died in election-related attacks.

Sputtering democracy

Nigeria, a country of 126 million people, has never seen a civilian government successfully hand over power to another. Though it is one of the world’s largest oil exporters, it is desperately poor and has a history of coups and unrest.

Obasanjo is a former military ruler who traded in his uniform for traditional robes and ran for election in 1999. His rule has brought limited improvement in individual and press freedoms. Yet the economy has stagnated, and critics say he has done little to fight poverty and corruption. Since he took office, 10,000 people have been killed in religious, political and ethnic fighting, including hundreds massacred by army troops.

The president has consolidated his ruling party’s lock on the three main levels of government. The party swept legislative elections. It also appeared to have a strong performance in a vote for state governors.

Buhari gained notoriety by launching a 1983 coup that toppled civilian leader Shehu Shagari after elections widely regarded as flawed.

Observers cite fraud

Foreign and local election observers have charged widespread vote fraud in some states in the south and east of Nigeria, yet stressed it was too early to say whether results nationwide had been compromised.

Max Van den Berg, the European Union’s chief election observer, said his group’s monitors witnessed ballot box stuffing and other “widespread election fraud” in six Nigerian states, including several in the restive southern swamps.

Van den Berg warned that if Nigerian authorities don’t investigate, “then the democratic process is in trouble.”

Two groups of American observers and a Nigerian group were similarly harsh in their reports. The Commonwealth Observer Group took a gentler tone.

Despite irregularities in some states, “in most of Nigeria, a genuine and largely successful effort was made to enable the people to vote freely,” the Commonwealth delegation’s leader, former African Union chief Salim Ahmed Salim, said.