beats by dre Two explosions have been heard off Yeonpyeong Island near the disputed  border in the Yellow Sea, South Korea's military says.In an interview  with ABC News on Tuesday, Obama called North Korea "a serious and  ongoing threat that needs to be dealt with.US President Barack Obama has  promised "unshakeable support" for South Korea following dr dre beats Seoul's exchange of artillery fire with North Korea on its western sea  border.       The US president meanwhile described South Korea as an important ally  and "a cornerstone of US security in the Pacific region.However, monster beats he reportedly ruled out any US military action against North Korea at  this stage.We're checking the origin of the sounds," a Joint Chiefs of  Staff spokesman told AFP on Friday.       On Tuesday, Seoul and Pyongyang exchanged artillery fire on the Yellow  Sea border monster headphones island of Yeonpyeong and each blamed the other side for starting the  skirmish.South Korea says it returned fire after North Korean forces  shelled one of its islands. But the North says the South fired first.  Two South Korean Marines were killed in the clashes hip hop beats.