WASHINGTON (Yonhap) -- U.S. President Barack Obama and his Russian counterpart, Dmitry Medvedev, agreed Monday that a North Korean long-range rocket launch, if carried out, would be a breach of U.N. Security Council resolutions that prohibit Pyongyang from being involved in ballistic missile activities.

At a meeting on the sidelines of a nuclear security summit in Seoul, the leaders also reaffirmed their commitment to diplomatic solutions to issues involving North Korea, Iran and Syria.

"And with respect to North Korea, we are going to be both sending messages to North Korea that they should not go forward with this missile launch, which would violate existing U.N. Security Council resolutions," Obama said after a bilateral summit with Medvedev. "And our hope is that we can resolve these issues diplomatically."

North Korea is subject to U.N. sanctions imposed after its nuclear and long-range missile tests in 2009. North Korea is banned from any launch using ballistic-missile technology.

The U.S. will apparently need Russia's cooperation in dealing with North Korea, especially if it launches a rocket in mid-April as it announced. Russia, along with China, has often sought to water down tough sanctions on Pyongyang sought by the U.S. and its allies.

The outgoing Russian leader said he discussed "all main issues" with Obama, but did not elaborate.

"We also spoke about the situation in the Middle East. We touched upon the Iranian nuclear program, the North Korean nuclear program, other sensitive issues -- Afghanistan cooperation," he said.