Russian scientists may be helping North Korea develop new missile systems designed to carry nuclear payloads.

That's according to a Bush administration official who doesn't want to be identified. The source says the missile program is based on Russian technology.

The official also says the technology's being tested by Iran (search), since North Korea has imposed its own test ban.

A leading military publication, Jane's Defense Weekly, has reported North Korea (search) is developing two new systems that "appreciably expand the ballistic-missile threat." But there are still a lot of unknowns, including whether those missiles could reach the U.S.

The Bush administration is working with South Korea, Japan, China and Russia to negotiate an agreement with North Korea to end its nuclear weapons program. Talks could resume next month.