SEOUL , South Korea ( CNN ) -- North Korea test-fired a fourth short-range missile off its east coast Thursday , South Korea 's Yonhap News Agency reported . North Korean leader Kim Jong Il 's administration has become more aggressive in recent months . South Korea 's Defense Ministry had earlier confirmed three launches , but could not immediately be reached about the fourth reported missile . The first three missiles were fired at 5:20 p.m. , 6 p.m. , and 7:50 p.m. local time from Sinsang-ni near the eastern coastal city of Wonsan , a ministry spokesman said . A U.S. official told CNN `` the missile firings come as no surprise . '' `` The North has been carrying out provocative acts for some time , '' said the official , who did not want to be named for security reasons . `` North Korea needs to stop this type of activity and return to the process of bringing about a denuclearization of the Korean peninsula . '' A U.S. intelligence official confirmed the test firings and said there are `` no indications whatsoever '' of an impending long-range missile test . The intelligence official , who could also not be named for security reasons , said the launches came as no surprise because North Korea had issued a warning to mariners to avoid an area in the Sea of Japan at certain times between June 24 and July 9 because of a `` military firing exercise , '' according to a U.S. military communication about the warning provided to CNN . The North issued a similar warning before testing a long-range missile in April , but that warning indicated two potential danger areas more indicative of a long-range missile test . Thursday 's reported test comes amid heightened tensions on the Korean peninsula . North Korea conducted a nuclear test in May , fired test rockets and threatened U.S. and South Korean ships near its territorial waters . Analyst Daniel Pinkston said the reported test might be training for a future test but it could also just be a routine military exercise . `` It is worrisome to some degree , but it is different from a ballistic missile launch , '' said Pinkston , of the International Crisis Group in Seoul , South Korea . `` It 's part of military training , but there seem to be no movements of troops or anything that would suggest preparations for military operations . `` So yes , people are watching it , the military is watching it here , but I do n't think it 's related to any plans or operations to attack anyone . '' Russia had a low-key reaction to the reported test . Russian military experts are carefully studying the reports but the launches will not change the political situation , a spokesman for Russia 's Foreign Ministry said . CNN 's Jill Dougherty in Moscow , Russia and Charley Keyes in Washington , D.C. , contributed to this report .
North Korea reportedly test fires four short-range missiles off its east coast . North Korean government issues warning to mariners ahead of launch . Comment: