Australia has joined the United States in condemning a treason charge filed by the Zimbabwe government against opposition leader Morgan Tsvangirai.

Australian Foreign Minister Alexander Downer told parliament Thursday the charges amount to harassment of the opposition leader. He says Australia is reserving the option of imposing sanctions against Zimbabwe's government.

Mr. Tsvangirai was formally charged Wednesday in a Harare court over an alleged plot to assassinate President Mugabe. An opposition member of parliament, Renson Gasela, was also charged. The two were released on bail.

On Wednesday, U.S. State Department spokesman Richard Boucher called the case part of a campaign of official retaliation by President Robert Mugabe against his political foes. Mr. Boucher said there is no convincing evidence to suggest a basis for the prosecution of Mr. Tsvangirai.

News of the treason probe broke shortly before last week's elections. Mr. Tsvangirai, who faces a possible death sentence, has strongly denied the allegation. Meanwhile, the Zimbabwe Congress of Trade Unions has begun a three-day strike to protest government treatment of opposition supporters. The government has declared the strike call illegal.

On Tuesday, the Commonwealth suspended Zimbabwe for one year saying the presidential election had not been free and fair. Mr. Tsvangirai's candidacy presented Mr. Mugabe with the stiffest challenge in his 22 years in power.

The Bush administration is consulting with the European Union and other governments about expanding targeted sanctions against Mr. Mugabe and his top officials in the wake of the election. Washington has already barred Mr. Mugabe and about 20 of his associates entry to the United States.

Some information for this report provided by AP and AFP.