Catalonia's regional police force admitted in a report several mistakes in its failed operation to arrest the region's fugitive former leader Carles Puigdemont in Barcelona earlier this month, Spanish media reported Friday.

Puigdemont, who fled abroad after leading a failed 2017 independence bid for Catalonia, defied an arrest warrant to return to Spain on August 8 to deliver a brief speech to thousands of people in Barcelona before fleeing the scene and returning to Belgium.

"That Mr Puigdemont would return to Spain and then flee was not contemplated as a possibility," the report, which was requested by Spain's Supreme Court, says, according to online newspaper El Confidencial.

A police drone that was following Puigdemont focused on the crowd which was advancing to the nearby Catalan regional parliament after he delivered his speech and lost track of him as he was getting into the car which took him away, the report added, according to Barcelona-based newspaper La Vanguardia.

Catalan police commissioner Eduard Sallent speaks to the press on Friday. Photo: AFP

Police communications were overwhelmed by misinformation about Puigdemont's location, and only one plainclothes officer managed to understand what was happening and run after the car, but was unable to immediately report it to his commanders, the report added, according to the newspaper.

Catalonia's regional police set up roadblocks across Barcelona after Puigdemont's appearance at the rally, but found no trace of him.

Three officers were later arrested on suspicion of helping Puigdemont escape, including one who allegedly owned the car he had used to leave the scene.

Puigdemont led Catalonia's regional government in 2017, when it pressed ahead with an independence referendum despite a court ban which was followed by a short-lived declaration of independence.

Spain's parliament passed an amnesty law in May for those involved in the secession bid, but the Supreme Court ruled on July 1 that the measure would not fully apply to Puigdemont.

In an opinion article published on news site Politico last week, Puigdemont said he took "a very big personal risk" by returning to Spain to "denounce the political obsession of a court that should be impartial".

"I didn't return to Catalonia to be arrested. I returned to exercise the right to resist oppression," he added.