The five nations trying to get North Korea to give up its nuclear weapons have not yet discussed involving the UN Security Council, South Korea has said.
The Yongbyon reactor has been at the centre of the nuclear row
Foreign Minister Ban Ki-moon said that efforts to resolve the impasse still rested with six-party negotiations.
His remarks came shortly after the US said that it would consider taking the matter to the Security Council if North Korea continued to refuse talks.
The US was responding to reports North Korea has shut a key nuclear plant.
South Korean officials said on Monday that operations at the Yongbyon plant had apparently been suspended - a move which analysts say could enable spent nuclear fuel to be reprocessed into weapons-grade plutonium.
In February North Korea admitted for the first time that it possessed nuclear weapons.
It also said it would not return to multi-lateral talks unless the US changed its "hostile" attitude towards Pyongyang.
Such bellicose statements have led Washington to grow increasingly impatient with Pyongyang.
On Monday White House spokesman Scott McClellan said the administration would discuss taking the issue to the UN Security Council.
"If they [the North Koreans] refuse to come back to the talks, then we will have to consult with our partners and look at the next steps," he said.
But referring to Mr McClellan's comments, Mr Ban said on Tuesday: "There has not been discussion about that at the South Korea-US government level."
South Korea has said in the past that all diplomatic options should be exhausted before the Security Council becomes involved.
The UN body might consider imposing economic sanctions against North Korea - a move Seoul is eager to avoid.
Since 2002, three rounds of discussions involving the US, Russia, the two Koreas, Japan and China have sought to ease tensions on the peninsula, with little success.
A potential fourth round was cancelled earlier this year after the North Korea said it was furious that US Secretary of State Condoleezza Rice had branded the nation an "outpost of tyranny".