British businessman Bill Browder, a prominent Kremlin critic, was detained and then released by Spanish police on Wednesday, after a warrant from Russian Federation for his arrest for tax evasion was found to be invalid, police said.
"Browder had an global arrest warrant issued by Russian Federation against him and that was the reason he was arrested", a Spanish National Police spokesperson told CNN.
Browder has led a campaign to persuade countries to adopt sanctions on Russian officials believed to be responsible for human rights abuses after the death of Magnitsky.
In December, a Moscow court sentenced Browder to nine years in prison in absentia on charges of tax evasion and funneling money overseas.
Browder helped push for the U.S.to pass the Magnitsky Act in 2012 - a bill which freezes the visas and assets of Russians suspected of human rights abuses by the United States government.
William Browder tweeted Wednesday that he was being arrested, posting a photo on his official profile saying that he was in the back of a Spanish police vehicle on the way to a police station.
But police later told AFP he had been released when they realised the "warrant" had expired. "This is the sixth time that Russian Federation has abused Interpol in my case".
One of Vladimir Putin's most vocal critics was briefly arrested in Spain on Wednesday morning after years on the run from the Russian government - but nobody wants to claim responsibility for doing it.
Minister of state at the Foreign Office, Sir Alan Duncan, said he was "deeply concerned to learn that the Russians have tried to get Bill Browder arrested in Spain".
But Browder countered that, telling City A.M.:"Interpol is playing a word game - there has never been a red notice, but there have been a number of diffusion notices - it just means it hasn't been officially approved".
Russian Federation allegedly tried so many times to arrest him, in fact, that Browder wrote a whole book about those attempts, titled Red Notice.
Browder is the founder of the Hermitage Capital fund, where Sergei Magnitsky had worked as a legal counselor before he died in a pretrial detention facility. "He is a British citizen and we will establish the full facts ASAP".
Foreign Secretary Boris Johnson said on Twitter after Mr Browder's release: "Just spoken to Bill Browder - very glad that he has now been released".
However, in a statement Interpol denied ever having an arrest warrant out for Browder.