North Korea test-fired four short-range missiles on Thursday, a South Korean Defence Ministry spokesman said.
Early Thursday evening, the ministry said, North Korea had test-fired two short-range missiles.
"One was fired at 5:20 p.m. and the other at 6 p.m. from Sinsang-ni," the Yonhap news agency quoted South Korean Defence Ministry spokesman Won Tae-jae as saying. Sinsang-ni is a North Korean town near the eastern coastal city of Wonsan.
Yonhap reported that the missiles appear to be of the surface-to-ship variety. The report contained few other details.
News cable channel YTN carried a similar report.
An unnamed defence ministry official — speaking condition of anonymity, citing department policy — later confirmed the North had fired another missile from the east coast.
Another official, who also requested anonymity, said the North fired one more rocket later Thursday. She provided no other details.
Yonhap, citing an unnamed military official, reported all four missiles flew about 100 kilometres and identified them as KN-01 missiles with a range of up to 160 kilometres.
"We had expected that they will fire short-range missiles at any time," South Korean Foreign Minister Yu Myung-hwan said while visiting the U.S. ambassador's residence.
"It's not a good sign, because they are demonstrating their military power."
In Tokyo, Japanese Prime Minister Taro Aso called the missile launches "provocative acts" and urged the North to refrain.
Earlier Thursday, the South Korean JoongAng Ilbo newspaper reported the North was likely to test-fire a number of missiles in the coming days, including ballistic Scud or Rodong rockets that are banned from testing under UN resolutions.
Tensions in the Korean peninsula have escalated steadily since May, when the North conducted an underground nuclear test and fired a spate of missiles.
Those moves prompted the United Nations Security Council to impose new sanctions on North Korea earlier this month.
Pyongyang has since issued a number of threats against the West and other Security Council members, and threatened to attack South Korea if it took part in the U.S.-led program to intercept North Korean ships suspected of carrying weapons.
North Korea fired off 4 small but loud missiles in honor of the USA's Fourth of July. Kim Jong II stated, Even if we have to starve 10 million more people to afford this display, it's well worth it to help America celebrate.