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HARARE, April 23 (Reuters) - Regional countries should mediate negotiations in Zimbabwe for a transitional government of national unity led by President Robert Mugabe to organise free elections and write a new constitution, a state-run newspaper said on Wednesday.

Political tensions make it impossible to hold a free and fair election run-off in the immediate term, said the editorial on The Herald's website.

"The current socio-economic environment in Zimbabwe is not conducive, and the country's political dynamics so distorted, that holding a free and fair election run-off in the immediate term is literally impossible," said the editorial.

Movement for Democratic Change (MDC) leader Morgan Tsvangirai has said he won the presidential election. He has accused Mugabe of attempting to rig victory in a probable runoff, which the party rejects.

Tsvangirai has repeatedly appealed to the Southern African Development Community (SADC) to intervene to guarantee a democratic poll result.

The MDC deprived Mugabe's ZANU-PF party of its majority in parliament in a parallel vote on March 29 but there has also been a delay to a partial recount of votes from that poll.

The recount could overturn the MDC victory. The opposition and Western governments say it is merely another ploy by Mugabe to steal back the election. (Reporting by MacDonald Dzirutwe)

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