North Korea fired three short-range missiles from its east coast on Saturday, South Korea's Defence Ministry said, prompting Western powers to urge Pyongyang to exercise restraint.
Launches by the North of short-range missiles are not uncommon but, after recent warnings from the communist state of impending nuclear war, such actions raise concerns about the region's security.
"North Korea fired short-range guided missiles twice in the morning and once in the afternoon off its east coast," an official at the South Korean Defence Ministry spokesman's office said by telephone.
The official declined to speculate on whether the missiles had been fired as part of a drill or training exercise.
"In case of any provocation, the ministry will keep monitoring the situation and remain on alert," he said.
A Japanese government source noted the three launches, but said none of the missiles had landed in Japan's territorial waters, the Kyodo news agency reported.
Tension on the Korean peninsula has subsided in the past month, having run high for several weeks after the United Nations Security Council imposed tougher sanctions against Pyongyang following its third nuclear test in February.
The North had for weeks issued nearly daily warnings of impending nuclear war with the South and the United States.
The United States declined to comment directly on the reported launches but said it was monitoring the situation.
"We continue to urge North Korea to exercise restraint and take steps to improve its relations with its neighbors," the State Department and the Pentagon said in a statement.
Britain's Foreign Office said: "We have been clear to North Korea that its long-term interests will not be served by threatening the international community and increasing regional tensions."
North Korea conducts regular launches of its Scud short-range missiles, which can hit targets in South Korea.
It conducted a successful launch of a long-range missile last December, saying it had put a weather satellite into orbit. The United States and its allies denounced the launch as a test of technology that could one day deliver a nuclear warhead.
During the weeks of high tension, South Korea reported that the North had moved missile launchers into place on its east coast for the possible launch of a medium-range Musudan missile. The Musudan has a range of 3,500 km, putting Japan in range and possibly the U.S. South Pacific island of Guam.