UPDATE 3-Uganda detains opposition leader again as president heads for vote win
* Police fire tear gas, stun grenades at Besigye party HQ
* Museveni, in power since 1986, in lead with 62 percent
* Opposition dispute early results, allege vote rigging (Adds detail, background)
By Edith Honan and Elias Biryabarema
KAMPALA, Feb 19 (Reuters) - Police detained Uganda's main opposition candidate Kizza Besigye for the third time this week and clashed with his supporters on Friday as early contested election results showed President Yoweri Museveni set to extend his 30-year grip on power.
Officers set off stun grenades and fired tear gas at crowds outside the headquarters of Besigye's Forum for Democratic Change (FDC), where senior members of the party accused organisers of rigging the vote.
Police later bundled Museveni's chief challenger into a van as the party was preparing to hold a press conference, a Reuters witness said. Officers said he was about to announce unofficial preliminary results - one commander said he had not been arrested but simply taken home.
Museveni, one of Africa's longest-serving leaders, has presided over strong economic growth, but faced mounting accusations at home and abroad of cracking down on dissent and failing to tackle corruption.
Other clashes broke out across the capital, and the spokesperson for another presidential contender, former prime minister Amama Mbabazi, said police had barricaded him in his home, stoking tensions a day after the vote. That report could not be confirmed independently. Continued...