The United Nations wants the South Sudan government to concentrate on peace efforts instead of preparing for elections.
Ms Bintou Keita, Assistant Secretary-General for Peacekeeping Operations, told Juba to refrain from organising elections before the revitalisation of the peace agreement.
South Sudan factions are expected to hold the last round of talks in May 17-21.
Ms Keita said in a statement that it was illogical for the young nation to organise any elections in the face of the worsening political and economic crises.
"The current political and economic situations in South Sudan are not conducive for free and fair elections," she said.
The Salva Kiir-led government recently announced that it would hold a General Election should the upcoming final round of peace talks fail to be fruitful.
"If nothing transpires from the upcoming revitalisation forum, the government will conduct an election to legitimise the leadership," Information minister and government spokesman Michael Makuei said.
But Ms Keita said the UN would not support the elections unless they are driven by the Intergovernmental Authority on Development (Igad)-led peace talks.
"The only plan is the high-level revitalisation forum."