North Korea fired three short-range guided missiles into its eastern waters on Saturday, in a move that could undermine diplomatic efforts to ease tensions on the peninsula. The North fired two missiles on Saturday morning and another in the afternoon, said a South Korean defense ministry spokesman, Kim Min-seok. He said Pyongyang's intent was unclear. North Korea routinely tests such missiles, but the latest move follows weeks of relative quiet on the peninsula, following a renewed bout of threats by the North earlier this year. The defense ministry said it was watching North Korea carefully, in case it conducts a provocation against South Korea. 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 United Nations 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. In the 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. In the past week, Glyn Davies, the top US envoy on North Korea, ended trips to South Korea, China and Japan. On Friday, an adviser to the Japanese prime minister, Shinzo Abe, returned from North Korea but didn't immediately give details of his talks with officials there. On Monday, North Korean state media showed that the country's hard-line defense minister had been replaced by a little-known army general.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 two 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 President Barack Obama warned North Korea against further nuclear provocations. Tension between the two Koreas remains high after both sides pulled out their workers from a jointly run factory complex earlier this year. The countries remain technically at war, after the 1950-53 Korean War ended in a truce instead of a peace treaty.