HARARE, Zimbabwe — Police fired tear gas and charged toward several hundred people on their way to a protest yesterday, challenging hopes for free and fair campaigning ahead of Zimbabwe’s national elections scheduled in March.

Police also briefly detained the leader of the opposition, Morgan Tsvangirai, opposition members said. Police Chief Superintendent Wayne Bvudzijena told South Africa’s SABC television news police just wanted to talk to Mr. Tsvangirai and two other opposition leaders “so we could establish what they intended to do today.”

Mr. Tsvangirai eventually addressed a few hundred people who managed to reach the protest site. The demonstration was the first test of new security laws meant to ease restrictions on protests in the run-up to elections.

“You have failed the test for a free and fair election. If this is the regime’s reaction, then elections are just a farce,” Mr. Tsvangirai said. He also said his Movement for Democratic Change party would intensify protests throughout Zimbabwe.

The opposition said Mr. Tsvangirai’s arrest and a ban on a march planned before the demonstration were a deliberate snub to South African efforts to find a solution to Zimbabwe’s political and economic crisis.

President Mbeki of South Africa mediated talks between the two sides after the opposition claimed security and press laws were hindering election campaigning. The negotiated changes to the laws were enacted January 11.