Zimbabwe ? Zimbabwe’s opposition party announced Thursday that it plans to boycott any runoff election with President Robert Mugabe. The move abruptly halted the political momentum toward a second and decisive round of balloting that many voters hoped would finally topple their president after 28 years in power.

Members of the opposition’s National Executive Committee voted unanimously that they believed their presidential candidate, Morgan Tsvangirai, won the March 29 vote by the clear majority needed for a first-round victory, said party spokesman Nelson Chamisa. A second round of voting, he said, would only encourage Mugabe to redouble efforts to rig the results and intimidate opposition supporters.

“We have resolved that we will not participate,” Chamisa said. “There won’t be any runoff. We have won.”

Chamisa declined to say how Tsvangirai intended to assume the presidency in a country with no history of peaceful transfers of power.