Spain'spublic prosecutor on Wednesday ordered a criminal probe of over 700 Catalan mayors who are cooperating with an October 1 independence referendum deemed illegal by Madrid.

The move increases the pressure on Catalan officials just one day before the pro-separatist camp officially kicks off its referendum campaign in the Mediterranean port of Tarragona.

The prosecutors' office ordered the mayors who have agreed to help stage the vote be summoned to court as official suspects and if they do not appear to "order their arrest", according to a copy of the ruling obtained by AFP.

Catalonia's pro-separatist government has asked the wealthy northeastern region's 948 mayors to provide facilities for polling stations for the plebiscite.

So far 712 mostly smaller municipalities have agreed to participate, according to a list posted on the website of Catalonia's Municipal Association for Independence (AMI) which represents 750 municipalities.

"They can arrest us, they're crazy!," David Rovira, the pro-separatist mayor of L'Espluga de Francoli, a town of some 3,800 residents, told AFP by telephone, adding that Madrid had "proposed nothing" to appease Catalonia's demands for greater autonomy.