North Korea threatened a "powerful" attack if the U.S. and South Korea proceed with joint military drills next month, warning Thursday that it could even resort to nuclear means.

The threat, routinely issued before South Korea and the U.S. embark on regularly scheduled military exercises, was made just hours after President Barack Obama's special envoy to North Korea arrived in Seoul to discuss the North.

Communist North Korea, believed to have enough weaponized plutonium to make at least a half-dozen atomic bombs, quit six-nation disarmament-for-aid negotiations last year. It also conducted a nuclear test, earning stricter U.N. sanctions.

China, the U.S. and other nations involved in the disarmament talks have been trying to draw North Korea back to the negotiating table.

U.S. envoy Stephen Bosworth met Thursday with South Korea's Wi Sung-lac after a stop in Beijing for talks with Chinese nuclear envoy Wu Dawei the previous day. During his Beijing visit, Bosworth called for the quick resumption of the nuclear negotiations with North Korea. He heads to Tokyo on Friday.

The North has demanded a lifting of the sanctions and peace talks with the U.S. on formally ending the 1950-53 Korean War before it returns to the negotiations.

"We believe the six-party talks are presented with a good opportunity to work out of the dilemma," Chinese Foreign Ministry spokesman Qin Gang told reporters, without elaborating.

South Korea and the U.S., which maintains 28,500 troops in South Korea, plan to conduct annual military exercises starting March 8.

The North sees the exercises as preparation for an invasion, but the U.S. and South Korea say the maneuvers are purely defensive.

"If the U.S. imperialists and South Korean warmongers launch the joint military exercises ... we will react to them with our powerful military counteraction, and if necessary, mercilessly destroy the bulwark of aggression by mobilizing all the offensive and defensive means including nuclear deterrent," a Korean People's Army spokesman said in a statement carried by the North's official Korean Central News Agency.

South Korea's Defense Ministry said it had no immediate comment on North Korea's threat.

The two Koreas technically remain in a state of war because their three-year conflict ended in a truce, not a peace treaty.