European football's governing body UEFA said on Thursday it was launching an investigation into claims Barcelona paid for favourable refereeing decisions.

UEFA said its ethics and disciplinary inspectors would probe "a potential violation of UEFA's legal framework by FC Barcelona in connection with the so-called 'Caso Negreira'", referring to the Spanish league's former refereeing chief Jose Maria Enriquez Negreira.

Barcelona have already been charged with corruption by Spanish prosecutors for payments between 2001 and 2018 to a company owned by Negreira, totalling around 7.3 million euros ($7.95 million).

The club say they were paying for reports and advice on refereeing but prosecutors have accused the club of seeking to gain favourable decision-making from officials.

Charges were filed earlier this month against the club, Negreira and two former Barcelona presidents, Sandro Rosell and Josep Maria Bartomeu, among others.

Negreira, a former referee, was the vice president of the refereeing committee of the Spanish football federation between 1994 and 2018.

The investigation began after Spain's tax authorities identified irregularities in tax payments made between 2016 and 2018 by the company Dasnil 95, owned by Negreira.

Dasnil 95 reportedly received payments from Barcelona between those years.

The last invoice was issued in June 2018. After that the refereeing committee was restructured and Negreira left the organisation.

Joan Laporta, the current Barcelona president, has insisted his club is innocent.

"Let it be clear Barca have never bought referees and Barca have never had the intention of buying referees, absolutely never," he said.

La Liga president Javier Tebas has previously said Barcelona faced no immediate danger because the governing bodies of Spanish, European and world football all have five-year statutes of limitations.

On the criminal level, the accused could face up to four years in prison. 

The case has caused tensions between Barcelona and old rivals Real Madrid, with the latter's president, Florentino Perez, not travelling to the Camp Nou for last weekend's Clasico, which was won by the Catalans.

Real Madrid have confirmed they will appear in the case as an "injured party" to defend their interests.

Relations between the two rival clubs seemed to be improving of late, as they looked to launch a European Super League project together in 2021 and remain set on the idea.