And joint military drills are underway with U.S. and South Korean forces. Tens of thousands of troops will participate.
The U.S. and South Korea conducted joint military drills on Tuesday, provoking North Korea to place its army in position.
More than 200 U.S. and South Korean troops participated in a guerilla warfare exercise in Pohang, south of Seoul, with the units practicing their rappelling skills in the snow.
[Lt. Col. Forrest Poole, U.S. Marines]: (English)
"The purpose of the training is to build a relationship and strengthen the relationship between the ROK (Republic of Korea) marine and the United States' marines. It's already good, but whenever we can work together, we can make it better."
The drills, aimed at testing the allies' defense readiness, draws fiery rhetoric from the North each year and fuel tensions on the Korean peninsula.
[Ji Soo-min, South Korean Colonel]: (Korean, male)
"We developed our capacity for joint battle and mountainous battle performances through this U.S. and South Korean joint military drill. It was a good chance to improve the friendship between South Korean and U.S. marines."
The drills involve about 18,000 U.S. troops, with 8,000 coming from abroad and 10,000 being already stationed in the South.
The South's Defense Ministry says about 20,000 of its troops will participate in the drills.