by STELLA KIM and TIM STELLOH
The missiles were fired at about 7:36 a.m. Monday (5:36 p.m. Sunday ET) and traveled about 620 miles, the official said. They landed in the East Sea, also called the Sea of Japan, the official said.
After calling a meeting of the National Security Council's Standing Committee on Monday morning, South Korea's acting president, Hwang Kyo-ahn, said the launch signaled "a real and imminent threat to the safety of our people."
Hwang called on the United States to complete the installation of the Terminal High Altitude Area Defense, an advanced missile defense system that the two countries announced on July 8 to counter North Korea's nuclear and missile programs.
After the announcement, North Korea's military threatened an unspecified "counter-action" that would turn the south into a "sea of fire."
Pyongyang on Friday threatened to conduct more missile tests in response to an annual two-month joint-military exercise between Seoul and Washington, which continues through April.