Kim's remarks during talks with Putin on Thursday appeared aimed at pushing Washington to be more flexible on North Korean demands for an easing of international sanctions.

U.S. President Donald Trump, who ended a second summit with Kim in February without a deal for North Korea to give up its nuclear weapons, seemed unperturbed, saying a lot of progress was being made toward an agreement and welcoming Putin's support.

Putin said after holding his first face-to-face talks with Kim in the Russian Pacific port of Vladivostok on Thursday that U.S. security guarantees would probably not be enough to persuade Pyongyang to give up its nuclear program.

He said he believed any U.S. guarantees might need to be supported by the other nations involved in previous six-way talks on the nuclear issue, which included Russia, China, Japan and South Korea as well as the United States and North Korea.