"In the context of the nuclear test conducted by (North Korea) on February 12th 2013, and the continued pursuit of certain nuclear activities by Iran ... the P5 reaffirmed their concerns about these serious challenges to the non-proliferation regime," they said in a statement.
The representatives of the United States, Russia, China, Britain and France - the five permanent members of the United Nations Security Council and longtime nuclear weapons states - made their statement at the end of a two-day preparatory meeting in Geneva ahead of the next review in 2015 of the Non-Proliferation Treaty (NPT).
That treaty has since 1970 set the global agenda for keeping countries from getting the bomb.
In their final statement, the so-called P5 stressed "the fundamental importance of an effective IAEA (International Atomic Energy Agency) safeguards system in preventing nuclear proliferation" and vowed to continue to work to "find peaceful diplomatic solutions to the outstanding problems faced by the non-proliferation regime."
Since launching its third nuclear test, North Korea, which withdrew from the NPT in 2003, has been locked in increasingly hostile exchanges with Seoul and Washington, including threats of nuclear war and precision missile strikes.
Iran, which remains a signatory of the NPT, is meanwhile believed to be working towards developing nuclear weapons, although the country insists its work is being conducted for energy and medical purposes.
Russia presided over this week's high-level diplomatic meeting. France will take the reins of next year's meeting aimed at preparing the 2015 NPT review conference.