Former Slovenian prime minister Janez Jansa and four others went on trial on Monday over alleged bribery in the former Yugoslav republic's biggest ever defence deal.

"All together it is just a farce," Jansa, prime minister from 2004-8 and now head of the main centre-right opposition Slovenian Democratic Party (SDS), told journalists as he arrived at Ljubljana's municipal court.

Jansa, 52, has been charged with "complicity in the giving or accepting bribery or bribery promises in exchange for a mediation" that led to the 2006 signing of a 278-million-euro ($392-million) deal with Finnish company Patria.

The other four defendants, among them a high-ranking defence ministry official, have also been charged with bribery.

The contract for 135 armoured vehicles was part of Slovenia's efforts to modernise its military after joining the NATO military alliance in 2004, the same year it became a member of the European Union.

Weeks before 2008 parliamentary elections, a Finnish television report alleged that several high-ranking Slovenian officials, including Jansa, had taken bribes from Patria.

Jansa has repeatedly slammed the accusations as "political" and has filed a private suit against Finnish television and the journalist who prepared the report, as well as against the Slovenian prosecutor who filed the case.

Presiding judge Barbara Klajnsek adjourned Monday's hearing due to the absence of one of the defendants, businessman Walter Wolf, over health reasons and scheduled a new hearing for next Monday.

"I'm afraid this farce will be a long-lasting one," Jansa told journalists after the hearing, reiterating the trial was aimed at weakening him politically.

"Those who filed the charges didn't do it expecting I would be found guilty, but hoping to have a long-lasting trial during which every Monday some 50 cameras will make pictures of me," Jansa said.

He added the trial would hamper his work as opposition leader since "having me in court every Monday gives my political rivals a great advantage in these times when the ruling coalition is falling apart."

Prime Minister Borut Pahor has announced he would seek a confidence vote later this month after two out of four partners quit his centre-left coalition last year, leaving him with a minority support in parliament.