French composer Didier Marouani has been detained in Moscow after a Russian pop star accused him of extortion.
Marouani and his lawyer were held at a bank where they said they hoped to meet the singer, Philipp Kirkorov, to settle a copyright issue out of court.
Instead they were met by police, after Kirkorov filed a complaint alleging Marouani, a founder of the band Space, tried to extort €1m ($1.1m) from him.
Marouani claims that Kirkorov - a huge star in Russia - plagiarised his work.
In a Facebook post on 1 November, the French composer complained that Kirkorov and composer Oleg Popkov had a huge hit with Cruel Love, a 2002 song that he said had partly been copied from his own composition Symphonic Space Dream.
Marouani's lawyer Igor Trunov said on Monday that Kirkorov had agreed to sign an agreement to pay compensation for use of his song.
But Kirkorov's lawyer Alexandre Dobrovinski denied that there had been any agreement and accused Marouani of extortion and slander.
Russian media reported that Marouani and Mr Trunov were released on Wednesday morning after being held overnight in a police cell.
Tass news agency quoted a law enforcement source as saying that police currently saw no reason to bring charges against the two, though no final decision had been taken.
However, Mr Trunov told Interfax news agency that they would now sue Kirkorov in a US court and that under US law the Russian singer was facing a minimum $10m payout.
Kirkorov, one of Russia's best known pop singers, was once described as Russia's Michael Jackson and is known to be an admirer of US President-elect Donald Trump.