LA PAZ, Bolivia, New York Times — Opposition groups in Bolivia called Tuesday for a nationwide general strike following violent protests over election results that seemed set to hand another term to long-time president Evo Morales.

President Evo Morales of Bolivia faced stinging accusations of election irregularities by international observers and violent protests in the streets on Monday as an updated tally of votes cast in the country’s presidential election appeared to give him a big enough lead to avoid a runoff.

With about 95 percent of the votes counted, election officials said Mr. Morales received 46.8 percent of the votes, while his closest rival, Carlos Mesa, won 36.7 percent. To avoid a runoff, the incumbent needed a 10-percentage-point advantage.

Preliminary results released hours after polls closed on Sunday showed a far tighter margin between the two leading candidates, an outcome that appeared to make it certain they would face off in a runoff in December.

Manuel González, the head of the election observer mission dispatched by the Organization of American States to monitor Bolivia’s vote, said on Monday night that he was “profoundly concerned” by the “drastic” reversal in the vote results.

Many Bolivians were suspicious of the result because election officials halted the updating of vote results for nearly 24 hours. Across the country, people posted videos on social media of scenes that purported to show electoral irregularities, including stashes of ballots and other election materials found in residences and vehicles.

The accusations of fraud created a widespread sense that the president or his allies had worked behind the scenes to rig the vote.

As election officials released new results at a hotel in La Paz giving the president a 10-percentage-point lead, opponents of Mr. Morales angrily changed “fraud, fraud!”

Heavily armed police officers were deployed to the streets, where they clashed with demonstrators on Monday night, according to television news reports.