A suspect has been remanded in custody for the "attempted terrorist assassination" of a co-founder of Spain's far-right Vox party, the High Court in Madrid announced Friday.

Alejo Vidal-Quadras, a former leader of Spain's main right-wing political party in Catalonia who went on to co-found Vox, was shot in the head in Madrid earlier this month.

"The judge has decided to remand the detainee in Lanjaron", in the south of Spain, "in custody for the offence of attempted terrorist assassination", the court said in a statement.

His girlfriend, arrested with him on Monday in Lanjaron, has been released on parole, as has a third suspect, arrested on Monday in the southern city of Malaga.

The three suspects are not "the direct perpetrators" of the crime, the police said in a statement.

The main suspect, accused of shooting the politician, is still being sought by the police, who have identified him as a "Frenchman of Tunisian origin with several previous convictions in France, his country of residence".

The three other suspects, one British and the others Spanish, are suspected of having provided logistical assistance, said police.

Vidal-Quadras was leader of the conservative PP party in the northeastern Catalonia region in the 1990s. He went on to be an MEP and then was among the founders of Vox, which he left shortly after its creation. 

Following the shooting on November 9, he was taken to Madrid's Gregorio Maranon hospital, which said in a statement on Thursday that he would be discharged after suffering a double fracture of the jaw.

Vidal-Quadras, who is close to the exiled Iranian opposition, has accused the leaders in Tehran of being behind the assassination attempt, according to those close to him.