Reports say North Korea has test-fired at least seven Scud-type ballistic missiles with a range of about 500km (312 miles).
South Korea and Japan called the latest tests, which follow several others in recent weeks, an "act of provocation", BBC News reports.
Commenting on this South Korea's Joint Chiefs of Staff said the military is fully ready to counter any North Korean threats and provocations.
The United States and North Korea's neighbors have described four North Korean missile tests Thursday as provocative, and called on the communist country to return to negotiations on de-nuclearization, Voice of America reports.
Professor Kim Yong-Hyun of Seoul's Dongguk University said the launches were clearly timed to coincide with US Independence Day.
"This is a thinly veiled warning to the United States and the international community that it may launch long-range missiles next time," he told AFP.
"The North is exercising salami tactics, firing short-range missiles on Thursday and launching missiles with longer range today," AFP reports.
It is assumed that the fighter will be created using new stealth technologies and have a very large interception range - up to 1,500 kilometers