Such scepticism came from Deputy Foreign Minister Lee Soo-Hyuck who met Chinese officials this week to prepare for a new round of six-way nuclear talks due to open in Beijing next month.
"Political situations are developing to make it difficult to reach an agreement," Lee told a meeting with South Korean businessmen, according to Yonhap news agency.
"I don't think the situation will allow the United States to reach an agreement one month before the presidential elections, and North Korea is also likely to want to see the outcome of the elections."
Top negotiators from the two Koreas, the United States, China, Russia and Japan are due to meet in Beijing by the end of September for new six-way talks aimed at resolving the nuclear stand-off.
But prospects have been overshadowed by the recent exchanges of insulting remarks against their top leaders between Washington and Pyongyang.