North Korea fired three short-range guided missiles into its eastern waters on Saturday, a South Korean official said.
The North fired two missiles on Saturday morning and another in the afternoon, South Korean defence ministry spokesman Kim Min-seok said. He said the North's intent was unclear and his ministry said it is watching North Korea carefully in case it conducts a provocation against South Korea.
North Korea routinely tests such missiles but the latest launches came during a period of tentative diplomacy aimed at easing tensions.
In March, North Korea launched what appeared to be two KN-02 missiles off its east coast. Experts believe the country is trying to improve the range and accuracy of its arsenal. North Korea recently withdrew two mid-range "Musudan" missiles believed to be capable of reaching Guam after moving them to its east coast earlier this year, US officials said. The North is banned from testing ballistic missiles under UN Security Council resolutions.
Earlier this year, North Korea threatened nuclear strikes on Seoul and Washington because of annual US-South Korean military drills and UN sanctions imposed over its third nuclear test in February. The drills ended late last month. This past month, the US and South Korea ended another round of naval drills involving a nuclear-powered aircraft carrier off the east coast. North Korea calls such drills preparation to invade the North.
Analysts say the recent North Korean threats were partly an attempt to push Washington to agree to disarmament-for-aid talks.
This past week, Glyn Davies, the top US envoy on North Korea, ended trips to South Korea, China and Japan. On Friday, an adviser to Japanese prime minister Shinzo Abe returned from North Korea but did not immediately give details of his talks with officials there.
On Monday, North Korean state media showed that the country's hard-line defence minister had been replaced by a little-known army general. Outside analysts said it was part of leader Kim Jong Un's efforts to tighten his grip on the powerful military after his father Kim Jong Il died in December 2011.
The United States and Japan are participants in six-nation nuclear disarmament talks along with the Koreas, Russia and Japan. North Korea walked out of the talks in 2009 after the UN condemned it for a long-range rocket launch.
North Korea possesses an array of missiles. US and South Korean officials do not believe the North's claim that it has developed nuclear warheads small enough to place on a missile. Last week in Washington, South Korean president Park Geun-hye and US president Barack Obama warned North Korea against further nuclear provocations.