Opposition officials say police forced their way into a house in suburban Harare that serves as the headquarters of a non-profit social welfare and health research agency. An aide to Mr. Tsvangirai said the leader of the Movement for Democratic Change and four advisers were discussing the party's future health policy.
The M-D-C says police claimed the meeting was illegal under the recently introduced Public Order Act, which forbids political meetings of more than two people unless four days notice is given to the authorities.
M-D-C officials say the director of the research agency was detained and questioned at Harare's main police station before being released without charge.
While police have acknowledged stopping the meeting, they have not commented on the allegation that the head of the health research agency was detained.
A spokesman for the M-D-C termed the police action "harassment designed to hinder Mr. Tsvangirai's presidential campaign." The M-D-C leader is the main challenger to President Robert Mugabe in the upcoming presidential election on March 9 and 10.
The M-D-C won a legal victory on Wednesday when Zimbabwe's Supreme Court, by a margin of four to one, ruled that recently passed General Laws Amendment Act, which gives the government more control over voting procedure, is unconstitutional.
Lawyers acting for the M-D-C said the main impact of the court decision will be to stop polling station supervisors, many of whom have been appointed by the army, from deciding which voters are allowed to cast their ballots during the two days of the election.
But the lawyers said Mr. Mugabe can use his presidential powers to overrule the Supreme Court.
In another development, the U-S embassy in Harare announced Wednesday that the United States is giving eight-thousand-400 tons of emergency food aid to the World Food Program to help combat Zimbabwe's worsening food crisis.
Joseph Sullivan, U-S ambassador to Zimbabwe, said the food situation is extremely serious.
We are now responding to the appeal by the United Nations for the neediest of the needy, those people who are hungry and suffering.
The World Food Program says up to half-a million people in Zimbabwe are in danger of starvation if they cannot get emergency food aid