Authorities in Zimbabwe have charged two more opposition officials with treason over an alleged plot to assassinate President Robert Mugabe. The charges come less than two weeks before closely fought presidential elections. A spokesman for the opposition Movement for Democratic Change says police charged the party's secretary general, Welshman Ncube, and a member of parliament, Renson Gasela, after summoning them for questioning. On Monday, police charged the opposition's leader, Morgan Tsvangirai, with treason for allegedly conspiring with a Canadian-based political consulting group to assassinate President Mugabe. Mr. Tsvangirai has denied the accusation, saying it is aimed at preventing him from challenging Mr. Mugabe in the March 9-10 presidential election. The United States has denounced the treason charges against Mr. Tsvangirai. State Department spokesman Richard Boucher said he knows of no convincing evidence to support the charges that come amid, what he called, a well-documented campaign of intimidation and violence against the opposition. Britain has also denounced the charges against Mr. Tsvangirai, and Australia Tuesday threatened to impose sanctions against Zimbabwe if the opposition leader is not allowed to compete in the presidential poll. Mr. Mugabe has been widely criticized for policies seen as stifling the political opposition and civil liberties ahead of the election.