SEOUL (Reuters) - Washington will use all available means outside the U.N. Security Council to isolate North Korea over its nuclear weapons program and counter its growing threat to world order, the U.S. envoy to the United Nations said on Sunday.

The United States will also use its military as a deterrent to the North's threat, Ambassador Samantha Power told a news conference in Seoul, after visiting the heavily armed Demilitarized Zone (DMZ) border between the rival Koreas.

"While Security Council resolutions are one tool in our tool box ... we are committed to using all the tools in our tool kit to address this serious threat including the diplomatic pressure that we are mobilizing around the world to convince other nations to isolate the regime," Power said.

Power's visit to the region, which included a stop in Tokyo last week, comes amid a push for tougher Security Council sanctions after the North's fifth nuclear test last month in defiance of a series of U.N. resolutions.

The United States and South Korea have been pushing governments around the world to take unilateral action including discouraging countries from using North Korean workers and ending visa waivers for North Koreans.

North Korea conducted its fifth and biggest nuclear test on Sept. 9 and South Korea has said it believes the North is ready to conduct another test at any time.

An increase in activity at the North's nuclear test site could signal preparations for a new test, a U.S.-based monitoring group, 38 North, said on Friday.

The North has defied U.N. sanctions since conducting its firth nuclear test in 2006 and has pressed ahead with the development of weapons programs including a range of ballistic missiles, which it says it needs for self-defense.

(Reporting by Jack Kim; Editing by Stephen Coates)