During an emergency meeting on Friday North Korean leader Kim Jong Un warned his rocket forces were ready "to settle accounts with the U.S."
He ordered his military to be prepared to strike the U.S. mainland and Hawaii. Thousands of soldiers marched in the streets in a show of support.
"We believe they are taking follow-up steps," said Kim Min-seok, spokesman of the South Korean Defense Ministry, referring to increased activities of the North Korean military units.
"South Korean and American intelligence authorities are closely watching whether North Korea is preparing its short, medium, and long-range missiles, including its Scud, Rodong and Musudan," Min-seok said.
But experts say it's unlikely they have the capability of striking America.
The latest tension began after the United States sent two B-2 stealth bombers from Missouri to South Korea and dropped dummy weapons in joint military drills with South Korea. That drill came just hours after North korea cut off communications with the South.