In the first US response to North Korea's test-firing of seven apparently Scud-type missiles early Saturday, State Department Karl Duckworth spokesman called on Pyongyang not to "aggravate tensions." Speaking to reporters on Saturday afternoon, Duckworth was quoted as calling the launches "not helpful," stressing that ""North Korea should refrain from actions that aggravate tensions and focus on denuclearization talks and the implementation of its commitments from the September 19, 2005 joint statement." A report from South Korean official news agency Yonhap on Saturday morning quoted a South Korean government official as saying that the ground-to-ground missiles were "estimated to have a range of 400-500km." The official evaluated that the missiles were more dangerous than previous missiles fired as they cover a longer range. South Korea's Joint Chiefs of Staff said in a statement that two missiles were fired between 8 a.m. (2300 GMT) and 8:30 a.m. (2330 GMT), and a third was fired later in the morning, though he did not comment on range or type. Israel Radio reported an additional three missiles were launched later Saturday, and another, the seventh overall, was fired on Saturday afternoon. US and South Korean intelligence estimated that the launches were deliberately timed to coincide with Fourth of July celebrations in the United States. "Our military is fully ready to counter any North Korean threats and provocations based on strong South Korea-US combined defense posture," the statement said. The Yonhap report also noted that other officials saw the test-launch as a "politically motivated move" connected to US Independence Day. North Korea's state news agency carried no reports on the launches. The chief of US Naval operations, Adm. Gary Roughead, said the American military was ready for any North Korean missile tests. "Our ships and forces here are prepared for the tracking of the missiles and observing the activities that are going on," Roughead said after meeting Japanese military officials in Tokyo on Saturday. On Thursday, North Korea fired a barrage of short-range missiles off its east coast. Pyongyang had earlier marked a large area of water off its east coast as a no-sail zone through July 10, citing military drills. Thursday's launches of four short-range missiles were believed to be the North's first military action in the designated zone.