Germany called for the European Union to consider imposing fresh sanctions on Belarus unless significant reforms are made in the wake of the allegedly rigged election.
Opposition candidate Svetlana Tikhanovskaya in her complaint to the Central Election Commission (CEC) demanded on Monday that the published results of the vote be declared void.
They said they were ready to hold talks with authorities.
Tikhanovskaya won 9.9%, while three other candidates each won less than two percent.
"I consider that we have already won because we've already conquered our fear, our apathy, our indifference", she said, calling on Lukashenko to step down.
Her ally, Maria Kolesnikova, said the government was "incapable of running the country" and an "unprecedented" political crisis was setting in.
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Huge queues had formed outside polling stations in the capital Minsk and other cities before voting ended at 8pm local time, after Tikhanovskaya urged her supporters to vote late to give authorities less chance to falsify the election.
Meanwhile, rights groups have said one person was killed and dozens injured in a police crackdown on protests that followed Sunday's polls. "Fundamental rights must be respected", he said in a statement.
Lukashenko, who was a collective farm manager under the Soviets, has repeatedly come under fire for his record on human rights through his five terms of office. Lukashenko has not yet commented on the results or the protests, only saying Monday that "the people" should be the cornerstone of any politics, according to the state news agency Belta. "I want them to have a future", said another protester.
The shirtless body of Yevgeny Zaichkin, 35, could be seen in Reuters images of protests in Minsk lying on a grassy patch of ground next to a street with a riot police officer in body armour standing over him and gesturing.
Foreign observers have not judged an election to be free and fair in Belarus since 1995, and the run-up to the vote saw authorities jail Lukashenko's rivals and open criminal investigations into others who voiced opposition.
Local media reported about the first death during the clashes.
Belarusians tired of the country's deteriorating economy and Lukashenko's repression of the opposition coalesced around Tsikhanouskaya, a former teacher and the wife of a jailed opposition blogger, in large shows of support unusual for a country where crackdowns on dissent are routine. He announced last month that he had been infected but had no symptoms and recovered quickly, allegedly thanks to playing sports.