South African President Jacob Zuma on Wednesday urged Zimbabwe's rival leaders to speed up political reforms seen as critical to avoiding another violent and disputed election, but President Robert Mugabe signalled he would not be pushed into endorsing a new constitution already accepted by his foes.Speaking to journalists after a series of meetings with Mugabe and his rival, Prime Minister Morgan Tsvangirai, Zuma said there was some progress on a new constitution, but minor hitches remained.Local political analysts say Mugabe's ZANU-PF, which was forced  into a power-sharing government with Tsvangirai's Movement for Democratic Change (MDC) following a disputed poll in 2008, is likely to stall agreement on a draft charter to reverse proposals eroding sweeping presidential powers.Zuma, who is mediating the Zimbabwe crisis, said he had discussed various issues with Mugabe, Tsvangirai and Welshman Ncube, leader of a small MDC wing."I think from what I have gathered, there has been some movement forward, although there are some hitches here and there, but they are not as major as they used to be," he said, adding that would report his findings to a summit of the 15-nation Southern African Development Community (SADC) in Mozambique this weekend.Zuma was in Harare on Wednesday to nudge the Zimbabwean leaders to agree to a plan for elections that are expected in the next year or two.Tsvangirai said they primarily discussed progress on a draft constitution recently presented to the rival parties after three years of political bickering. He noted Mugabe's party had yet to endorse the proposed charter.Asked if the final decision on the constitution will be made by the leaders of the coalition parties, Tsvangirai, who accuses Mugabe of rigging elections to retain power, said there was no such provision in their power-sharing agreement.