Secretary-General Ban Ki-moon has congratulated leaders of the Southern African Development Community for holding a summit this weekend on the post-electoral crisis in Zimbabwe. Zimbabwean electoral officials are not saying whether President Robert Mugabe or opposition leader Morgan Tsvangirai won March 29 presidential elections. UN deputy spokeswoman Marie Okabe said Friday that Ban is "concerned that the situation in Zimbabwe could deteriorate if there is no prompt action to resolve this impasse." Zambian President Levy Mwanawasa has called an emergency summit of regional leaders for Saturday in the capital, Lusaka, to discuss the crisis. He is the only southern African leader to publicly criticize Mugabe's policies.