* Seat needs alternative options if diesel bans come
* Porsche also says no good desperately holding on
* German ministers call for transparency, co-operation
FRANKFURT, July 22 (Reuters) - Carmaker Seat sees compressed-natural-gas (CNG) as an alternative fuel to diesel, the chief executive of the Spanish Volkswagen division said on Saturday.
Seat was betting on CNG in order to compensate for falling diesel car sales, its chief executive Luca de Meo was quoted as saying in part of a report due to run in full in the July 24 issue of Automobilwoche.
"We have to offer customers a sensible solution. The debate about diesel is continuing and therefore we need other options, he said.
While Seat, bought by Volkswagen in 1986, was less exposed to diesel dependency than premium carmakers, it still had to observe market dynamics very carefully, de Meo said.
"If the mayor of Barcelona decides to close the city centre for Euro-6-diesels, then customers will probably no longer buy diesel cars," he said.
The finance chief of sister company Porsche, Lutz Meschke, also interviewed, said that discussions about a diesel-free future were underway.
"In our segment, we have the right answers with plug-in hybrids and purely electrical drives. Why should I anxiously hold on to a diesel?" he said.
UNDER PRESSURE
Car stocks tumbled on Friday after a report in Der Spiegel that VW, BMW, Audi and Porsche may have colluded to fix the prices of diesel emissions treatment systems.
The Spiegel report said that cartel-like behaviour may have also applied to vehicle developments, brakes, petrol and diesel engines, clutches and transmissions, citing a letter sent to cartel authorities.
The companies have not commented on details and only referred to speculation with regard to the report, while Transport Minister Alexander Dobrindt said it was now up to antitrust authorities to study the allegations.
"The cartel authorities must investigate, study the accusations in detail and, where necessary, must draw consequences," he said in remarks to Reuters.
"Cartel behaviour would be an additional burden for the (diesel) subject matter that we are currently involved in with the car industry," Dobrindt said.
German Economy Minister Brigitte Zypries, in separate remarks, echoed this, adding that trust in the entire German automotive industry was at stake.
"Everyone is well advised to cooperate with the state institutions and to create transparency," she said.
The European Commission said on Saturday that EU antitrust regulators were investigating the allegations. (Reporting by Christian Kraemer and Vera Eckert; Editing by Andrew Bolton)