The death toll from Zimbabwe's cholera outbreak has risen sharply, the United Nations said Wednesday, reporting 775 deaths and 16,141 cases of the waterborne disease in the southern African nation. Cholera has spread rapidly in Zimbabwe because of the country's crumbling health care system and the lack of clean water. Last week, Zimbabwe declared a health emergency because of cholera and the collapse of its health services. The latest figures from the World Health Organization show a jump of nearly 200 deaths from Tuesday, when the UN humanitarian office reported that 589 people had died out of 13,960 cases. Zimbabwe's government says the disease is under control but aid agencies warn that coming rains could spreading cholera further in a population already weakened by disease and hunger. With hundreds of people fleeing the country to seek treatment, cholera has already spread to Zimbabwe's neighbors. Nine deaths were reported Tuesday in South Africa. President Robert Mugabe is coming under increasing pressure as concern about the country's deepening humanitarian and political crisis mounts. President George W. Bush, British Prime Minister Gordon Brown and French President Nicolas Sarkozy have all called recently for the 84-year-old leader to step down. Also Wednesday, a group of lawyers marched peacefully through downtown Harare calling for the release of human rights activist Jestina Mukoko. Mukoko, director of the Zimbabwe Peace Project, was allegedly taken from her home a week ago when activists held nationwide protests against the country's deepening economic and health crises. Zimbabwean security officials regularly detain, harass and beat opponents of Mugabe's increasingly autocratic rule, although the government denies such allegations. A judge ordered police Tuesday to investigate Mukoko's disappearance. The lawyers - some dressed in their black gowns - carried placards reading: "Stop abductions now" and calling Mukoko a "woman of peace." The opposition Movement for Democratic Change said in a statement that at least 20 activists were missing. A number of international and regional organizations, including South Africa's ruling party, also were raising concerns about the whereabouts of the activists. The African National Congress urged Zimbabwe's government to find them "as a matter of urgency." Irene Khan, secretary-general of Amnesty International said human rights abuses were worsening in Zimbabwe as Mugabe's regime was "desperate" to stay in power. In Oslo, Norway, on Wednesday, Nobel peace laureate Martti Ahtisaari criticized Mugabe, saying the international community failed to meet its obligation to intervene when "something goes terribly wrong, as it has." "(Mugabe) was the hope of the continent after Zimbabwe was born. How this desire for absolute power make somebody behave the way he has done? I feel very sad about that," he said. Mugabe, 84, has ruled his country since its 1980 independence from Britain and has refused to leave office following disputed elections in March. A power-sharing deal worked out in September with the opposition has been deadlocked over how to divvy up Cabinet posts.