With no substantive comment from either side after three weeks of negotiation, the progress of power-sharing talks between the leader of the Zimbabwean regime, Robert Mugabe, and his opposition rival, Morgan Tsvangirai, remain a mystery. But some hint of the atmosphere in which they are being conducted emerged Thursday when Zimbabwean security forces briefly detained Tsvangirai, his deputy -- Movement for Democratic Change (M.D.C.) general secretary Tendai Biti -- and a third M.D.C. official. The three were held at Harare airport and, after their passports were confiscated, prevented from leaving the country to attend a weekend summit of southern African leaders in Johannesburg, South Africa. Biti said the incident raised questions about the Mugabe regime's true intentions. "This is a reflection of their insincerity," he told reporters at the airport. "They want to talk to us. Yet they behave like hooligans."