Zimbabwe's opposition leader is calling for UN peacekeepers to help prepare the way for new elections in his country. Morgan Tsvangirai, in an opinion piece published Wednesday in London's The Guardian newspaper, says such intervention offers Zimbabweans the "best chance" to express their choice at the ballot box. Tsvangirai has pulled out of a presidential runoff against President Robert Mugabe scheduled Friday, saying violence unleashed by Mugabe has made the vote impossible. Tsvangirai remains at the Dutch Embassy in Harare, where he has been since announcing his withdrawal on Sunday. Mugabe insists Friday's vote will go ahead.