BRUSSELS, Feb 22 (Reuters) - Belgium's justice minister on Tuesday rejected police calls for permission to tap soccer hooligans' mobile phones during the European Championship Finals to prevent them organising riots.

Minister Marc Verwilghen told a parliamentary committee the idea had been considered but rejected for legal reasons. 'To place a telephone under surveillance a warrant is required from an investigating judge. This would stop us being able to act in a proactive fashion,' Verwilghen said.

Police said at the weekend that listening to mobile phones could be a key weapon against hooligans at the tournament to be hosted jointly by Belgium and the Netherlands in June and July.

The mobile phone has become widely used by troublemakers to pass on information and rally 'troops' to hastily arranged clashes, giving the authorities little time to respond.

In March 1997 one Dutch soccer fan died after rival Ajax Amsterdam and Feyenoord Rotterdam supporters fought a pitched battle planned by mobile phone.

Genk police commissioner Marc Geerits told Belgian daily De Morgen on Saturday that police would seek swift legal backing for a special waiver of existing phone tapping restrictions if there was any serious trouble.