Harare, Zimbabwe ? Just days before the presidential vote, the main challenger to President Robert Mugabe was charged Monday with the capital offense of treason for allegedly plotting to assassinate the Zimbabwe leader.

Morgan Tsvangirai denied the allegations and pledged to continue campaigning for the March 9-10 elections, the most contentious since the country gained independence in 1980.

“This whole thing is contrived to damage me politically. The timing is obvious,” Tsvangirai told reporters. “This was all along ZANU-PF’s (the ruling party) strategy to eliminate me from the race.”

Mugabe, the southern African nation’s only leader since winning independence from Britain, is fighting for his political survival as Zimbabwe’s economy collapses and political violence rages.

Police questioned Tsvangirai, president of the Movement for Democratic Change, Zimbabwe’s main opposition party, for two hours Monday. He was charged with treason, released and told he would be summoned later, he said. Treason convictions carry the death penalty in Zimbabwe.

In Washington, the State Department said the charge “falls against a backdrop of a very well-documented campaign of violence and intimidation against the opposition.”

“We’re aware of no convincing evidence that there’s any basis for these allegations,” spokesman Richard Boucher said. He said the allegations appear to be another example of Mugabe’s “increasingly authoritarian rule” and his government’s “apparent determination to intimidate and repress the opposition.”