SEOUL (AFP) -- The U.S. and South Korean defense chiefs expressed concern Wednesday at North Korea's development of long-range missiles and other weapons of mass destruction, Yonhap news agency said.

It said U.S. Secretary of Defense Robert Gates and Defense Minister Kim Jang-Soo made the remarks in a draft joint statement to be released later Wednesday at the end of an annual security meeting.
The Defense Ministry told AFP it was unaware of the draft.
""The Secretary and the Minister agreed that North Korea's continued development of weapons of massive destruction and long-range missiles, along with the danger of proliferation, were a challenge to the ROK (South Korea)-U.S. Alliance,"" Yonhap quoted the draft as saying.
The defense chief also reaffirmed Washington's commitment to provide a nuclear umbrella for South Korea against North Korea, Yonhap said.
""Secretary Gates offered assurances of firm U.S. commitment and immediate support towards the ROK including continuation of the extended deterrence offered by the U.S. nuclear umbrella, consistent with the ROK-U.S. Mutual Defense Treaty,"" it quoted the draft as saying.
North Korea, which staged a nuclear test in October 2006, on Monday began disabling its nuclear program under U.S. supervision as part of a six-nation accord. It has not yet agreed arrangements for handing over its plutonium stockpile and any other nuclear devices.
The United States has accused North Korea of being a leading global proliferator of missiles. But the cash-strapped country has refused to stop the exports, a major source of hard currency earnings.
In July last year the North test-fired seven missiles, including the Taepodong-2 which in theory could reach the U.S. west coast.