A top South Korean diplomat says a U.S. announcement last week on North Korea's suspected nuclear collaboration with Syria has raised proliferation concerns.

The nation’s chief nuclear negotiator Kim Sook made the statement to reporters before leaving for the United States on Sunday to meet with his U.S. counterpart Christopher Hill.

Kim stressed the need to address concerns surrounding the North’s plutonium and suspected uranium enrichment activities as well as nuclear proliferation.

He also said both Seoul and Washington agree on the need for the Korean Peninsula to be nuclear-free after all of the North’s nuclear programs are completely disclosed and verified.

Kim’s comments come after the White House announced Friday it's convinced North Korea has helped Syria pursue a covert nuclear program.