MINSK, Belarus – Assailants attacked an aide to the opposition leader in Belarus on Thursday after state TV broadcast a recording of an alleged conversation in which he consulted with a Polish NGO on protest strategies, an opposition spokesman said.

The beating was among the latest incidents in what opposition leader Alexander Milinkevich called a campaign of persecution against Belarusians challenging authoritarian leader Alexander Lukashenko’s re-election.

The vote has been denounced by his domestic opponents and Western critics as deeply undemocratic. Belarusian election officials have rejected formal opposition complaints challenging the vote.

Viktor Korniyenko, a deputy chief on Mr. Milinkevich’s staff, was beaten by two assailants in the entranceway to his apartment building, Mr. Milinkevich spokesman Pavel Mazheika said. The attackers clubbed Mr. Korniyenko on the head and he was hospitalized in serious condition, Mr. Mazheika said.

On Wednesday, state-run TV broadcast what it characterized as a recorded phone conversation between Korniyenko and a representative of the Batory Foundation, a Poland-based non-governmental organization that has conducted democracy support programs in Belarus.

The representative told Mr. Korniyenko that opposition leaders should not urge a halt to protests on Oktyabrskaya Square and should boost the size of the protest tent camp where young demonstrators are maintaining a constant vigil, according to a transcript of the alleged conversation.

It was printed yesterday on the front page of the newspaper published by Mr. Lukashenko’s administration.

The state-media reports about the alleged conversation fit in with Mr. Lukashenko’s repeated claims that the opposition is supported by Western forces seeking to bring him down and control Belarus. State TV has also broadcast reports saying the protests are financed by Western embassies, allegations the diplomatic missions deny.

The Central Election Commission yesterday declared Mr. Lukashenko the official winner of Sunday’s election, saying final results showed he received 83% of the votes, compared to 6.1% for Mr. Milinkevich, the state news agency Belta reported. The official results differed little from preliminary results issued Monday.

Mr. Milinkevich says Mr. Lukashenko’s official tally is “monstrously inflated” and is calling for a new vote.

Early yesterday, he told tent camp residents entering the fourth day of a round-the-clock vigil that they had defied expectations by maintaining their vigil as long as they have.