The South Korean military said North Korea fired several projectiles off its eastern coast early Monday in what appears to be the second launch in a month.
South Korean officials said the missiles flew about 1,000 kilometers, or 620 miles, into waters off its east coast.
CNN reported that North Korea fired four ballistic missiles.
The tests come as leader Kim Jong Un pushes for a nuclear and missile program that can deter what he calls U.S. and South Korean hostility toward the North.
NBC News reported that a missile was fired about 7:36 a.m. Monday local time, or 5:36 p.m. ET on Sunday, according to a South Korean military official. South Korea's acting president, Hwang Kyo-ahn, called for an immediate meeting of the National Security Council's standing committee, NBC reported.
North Korea on Friday threatened to conduct more missile tests in response to the two-month Foal Eagle exercise between Seoul and Washington, which continues through April.
South Korea's Joint Chief of Staff said in a statement that Monday's launches were made from the Tongchang-ri area in North Pyongan province. The area is the home of the North's Seohae Satellite Station, where it has conducted prohibited long-range rocket launches in recent years, AP reported.
Pyongyang's launch in mid-February of a medium- to intermediate-range missile was aimed at drawing global attention to the North by boasting its nuclear and missile capabilities, South Korea’s defense ministry said at the time. "It is also believed that it was an armed provocation to test the response from the new U.S. administration under President Trump."
That launch came as Trump was hosting Japanese Prime Minister Shinzo Abe at his Mar-a-Lago estate in Florida.
NATO Secretary General Jens Stoltenberg last month urged North Korea "not to raise tensions further and to re-engage in a credible and meaningful dialogue with the international community." The European Union said in a statement that North Korea's "repeated disregard of its international obligations is provocative and unacceptable.”
The United States has 28,500 troops stationed in South Korea as a deterrent against a potential aggression from the North.
Contributing: Aamer Madhani. Follow Greg Toppo on Twitter: @gtoppo