The United States and South Korea offered on Saturday to keep their end of a defunct 2005 aid agreement with North Korea, provided Pyongyang took take "meaningful steps" to denuclearize.
In a joint statement released as U.S. Secretary of State John Kerry wrapped up his first visit to Seoul, the two sides appeared to put the accent on diplomacy after weeks of threatening rhetoric from Pyongyang.
"North Korea must adhere to its international obligations and commitments or face further isolation," the statement said.
"We will continue to encourage North Korea to make the right choice. If North Korea does so, we are prepared to implement the commitments under the 2005 Six-Party Joint Statement," it added, referring to the aid-for-denuclearization agreement.
"But Pyongyang must prove its seriousness by taking meaningful steps to abide by its international obligations," it said.
The United States and its allies believe the North violated the 2005 deal by conducting a nuclear test in 2006 and pursuing a uranium enrichment program that would give it a second path to a nuclear weapon in addition to its plutonium-based program.
At a news conference with South Korean Foreign Minister Yun Byung-se on Friday, Kerry said the United States wanted to resume talks about North Korea's earlier pledges to halt its nuclear program.
But he also stressed that Washington would defend its allies in the region if necessary and pointedly said that Kim Jong-un, the North Korean leader, "needs to understand, as I think he probably does, what the outcome of a conflict would be."
North Korea has issued weeks of shrill threats of an impending war since the imposition of U.N. sanctions in response to its third nuclear test in February.
North Korea has repeatedly said it will not abandon nuclear weapons which it said on Friday were its "treasured" guarantor of security.
Kerry's visit coincided with preparations for Monday's anniversary of North Korean state founder Kim Il-Sung's birth, a possible pretext for a show of strength, with speculation focusing on a possible new missile test launch.
Kerry, who flies to China on Saturday and to Japan on Sunday, told the news conference that if North Korea's 30-year-old leader went ahead with the launch of a medium-range missile, he would be making "a huge mistake."