Barcelona: Barcelona have given their full backing to Lionel Messi in the Argentina forward's tax fraud case and vowed to fight "external decisions" they say are unfairly targeting the club.

A Spanish court on Thursday ordered Messi and his father Jorge, who are accused of defrauding the Spanish state of 4.2 million euros ($4.76 million) from 2007 to 2009, to stand trial and the state attorney said Barca's star player should serve a jail sentence of up to 22 months if found guilty.

In a statement published late on Thursday, Barca noted the state attorney's stance was "the complete opposite" to that of Spain's public prosecutor, who has said Lionel Messi should not have to answer the charges as his father oversaw his finances.

"FC Barcelona has expressed its affection and solidarity to Leo Messi and his family in such a peculiar situation," the statement said.

"The club shall continue to offer him and his family its full support and assistance in the legal, fiscal and administrative aspects of these proceedings."

Messi is one of several Barca players, including compatriot Javier Mascherano and Brazil forward Neymar, who have been targeted by the Spanish authorities in recent months. All deny wrongdoing.

The club itself was charged last year with tax fraud in the signing of Neymar from Brazilian club Santos and paid $18.6 million in what it called a "complementary tax declaration".

They said they remained "convinced the original tax payment was in line with their fiscal obligations".

Barca's legal problems have come on top of a FIFA ban for breaking rules on the signing of minors and president Josep Maria Bartomeu complained last year of what he called a concerted campaign to damage the Spanish and European champions.

He was repeatedly asked who was behind the alleged campaign, including if it might be arch rivals Real Madrid, but he declined to provide any names.

"FC Barcelona condemns the accumulation of totally inadmissible and external decisions that have been going on for some time and that have nothing to with strictly sporting affairs," Barca said on Thursday.

"They are damaging to the smooth running of the club, its stability and that of the players that form part of it.

"The club shall be working with more determination than ever to defend its legitimate rights and is ready for any new challenges that might arise."