The former chief of Catalonia's police force, Josep Lluis Trapero, has been charged over events linked with last year's independence referendum.

He faces two Spanish counts of sedition and one of criminal organisation.

Other former regional officials were also charged by investigating judge Carmen Lamela. She accuses them of co-operating with an organised plan to seek Catalonia's secession.

Spain's constitutional court ruled the 1 October referendum illegal.

It is another setback for those who support the establishment of an independent state.

Many of the movement's most prominent figures face charges and some are in detention or the subject of arrest warrants.

The movement's former leader, Carles Puigdemont, is in a German jail while judicial authorities consider a Spanish extradition request.

The charges faced by the accused relate to events on 20 and 21 September, when crowds tried to obstruct Spanish police raiding devolved ministry buildings in a bid to prevent the referendum, and the 1 October referendum itself.

Judge Lamela alleged that Major Trapero's force adopted a passive stance to avoid taking action against the organisers of the independence drive and failed to respond to requests for help from the Civil Guard, who were acting on the Madrid government's orders.

In addition, she said, his force had leaked their action plans to those organising the referendum.

Two more members of the regional police and an official with the regional interior department were also charged with sedition - under Spanish law, preventing officers of the law from properly executing their duties.

The four accused are scheduled to testify before the judge on 16 April.