Spain's Supreme Court has denied a request by a Catalan separatist leader to leave jail so he can become a European Parliament member after being elected last month.

The court said Friday that Catalonia's former vice president Oriol Junqueras will not be allowed to attend a session on Monday at the Spanish Parliament where elected candidates to the European Parliament must swear to uphold the Spanish Constitution.

It says that, having sworn the oath, Junqueras would then have to take possession of his European Parliament seat, and that is impossible since he is in custody as he is considered a flight risk.

Junqueras, who was elected in May 26 elections, is one of a dozen separatists on trial for their role in a 2017 secession attempt by northeastern Catalonia.