BELARUS'S MAIN OPPOSITION LEADER ALEXANDER MILINKEVICH WAS BRIEFLY DETAINED BY POLICE ON WEDNESDAY, HIS SPOKESMAN SAID, BUT IT WAS UNCLEAR ON WHAT GROUNDS, REUTERS REPORTED. MILINKEVICH, WHO WAS THE MAIN LIBERAL RIVAL TO PRESIDENT ALEXANDER LUKASHENKO IN PRESIDENTIAL ELECTIONS THIS YEAR, WAS DRIVING OUTSIDE THE CAPITAL MINSK WHEN HIS CAR WAS STOPPED AND SEARCHED. HE WAS THEN DETAINED, SPOKESMAN PAVEL MOZHEIKO SAID. MILINKEVICH, HIS WIFE AND TWO OPPOSITION COLLEAGUES SPENT ABOUT THREE HOURS IN THE POLICE STATION IN POLOTSK, A SMALL TOWN SOME 250 KM (155 MILES) FROM MINSK, BEFORE THEY WERE RELEASED, OPPOSITION ACTIVIST VINTSUK VECHORKA TOLD REUTERS. "NO EXPLANATIONS WERE GIVEN TO THEM," HE SAID. MILINKEVICH HAS ALREADY SERVED A 15-DAY SENTENCE FOR PUBLIC ORDER OFFENCES IN MAY -- PART OF A GENERAL CRACKDOWN ON DISSENT IN BELARUS. TWO WEEKS AGO, ALEXANDER KOZULIN, THE OTHER OPPOSITION RIVAL TO LUKASHENKO IN THE MARCH POLL, WAS SENTENCED TO 5 1/2 YEARS IN PRISON FOR HIS ROLE IN ORGANISING PROTESTS AGAINST THE RESULT. LUKASHENKO, IN POWER SINCE 1994, IS CRITICISED BY WESTERN GOVERNMENTS AND THE OPPOSITION FOR OPPRESSING HIS POLITICAL RIVALS AND SILENCING THE INDEPENDENT MEDIA. THE UNITED STATES AND THE EUROPEAN UNION BOTH DENOUNCED HIS RE-ELECTION IN MARCH AS FRAUDULENT AND SLAPPED VISA BANS ON THE VETERAN LEADER AND HIS TOP OFFICIALS. LUKASHENKO DISMISSES ALL CRITICISM AND SAYS HE PROVIDES STABILITY. HE WAS CREDITED WITH 83 PERCENT IN THE POLL WHILE MILINKEVICH GOT ONLY ABOUT 6 PERCENT.