ROME (Reuters) - Italy"s antitrust regulator said on Friday it was opening an enquiry into airlines Easyjet EZJ.L, Ryanair RYA.I, Blue Panorama and Vueling for offering vouchers and not refunds to passengers whose flights were cancelled due to Covid-19. The regulator said that similar investigations had been opened in July against Italian carrier Alitalia [CAITLA.UL] and Volotea and that complaints from customers on the issue were rising. The watchdog said the cancelled flights were not during periods in which governments had imposed limits on movement between countries and that refunds of the tickets - an option envisaged by European rules - had not been offered.