Zimbabwe opposition leader Morgan Tsvangirai has gone to police headquarters in Harare to answer questions about an alleged plot to assassinate President Robert Mugabe.
A spokesman for the opposition Movement for Democratic Change says Mr. Tsvangirai was ordered to appear for questioning Monday.
The government says the opposition leader met with members of a Canadian-based political consulting group last year to arrange Mr. Mugabe's assassination. The ruling ZANU-PF party says it has a videotape of the meeting in Montreal that incriminates Mr. Tsvangirai.
Mr. Tsvangirai denies the allegation, calling it an attempt by the president to derail his election campaign before the vote March 9-10.
The opposition leader poses the stiffest challenge to Mr. Mugabe's 22-year hold on power.
Mr. Mugabe has been widely criticized for policies seen as stifling the political opposition and civil liberties ahead of the upcoming election.
On Sunday, a van carrying international election observers was attacked by youths after it left an opposition campaign rally in Chinhoyi, a stronghold of Mugabe supporters about 100 kilometers north of the capital.