The launches, which came two days after North Korea fired four short-range cruise missiles, will likely further escalate tensions in the region as the U.S. tries to muster support for tough enforcement of the latest U.N. Security Council resolution imposed on the communist regime for its May nuclear test.
South Korea's Joint Chiefs of Staff said three missiles were fired early Saturday, a fourth around noon and three more in the afternoon. The Defense Ministry said that the missiles were ballistic and are believed to have flown more than 250 miles.
"Our military is fully ready to counter any North Korean threats and provocations based on strong South Korea-U.S. combined defense posture," the Joint Chiefs of Staff said in a statement.
South Korea's Yonhap news agency quoted military officials as saying the missiles appeared to be a type of Scud missile. North Korea's Scuds are considered short-range, the South's military said.
But Yonhap also said that it is possible they could have been longer-range Rodong missiles fired a shorter distance.
Scud missiles have a range of up to 300 miles, which could hit most of South Korea. The Rodong has a range of up to 800 miles, putting most parts of Japan within striking distance.
North Korea is not allowed to fire Scuds, medium-range missiles or long-range missiles. They are banned under U.N. resolutions, including Resolution 1874 passed after North Korea's May 25 nuclear test, that prohibit any launch using ballistic missile technology.
Thursday's launches, on the other hand, did not violate the resolution as they were cruise missiles rather than ballistic, according to South Korea's Foreign Ministry.
Ballistic missiles are guided during their ascent out of the atmosphere but fall freely when they descend. Cruise missiles fly low and straight to their target.
The North has a record of timing missile tests for the U.S. national day, which fell on Saturday.
"The missiles were seen as part of military exercises, but North Korea also appeared to have sent a message to the U.S. through the missile launches," a senior official in South Korea's presidential office said, without elaborating.
The official told The Associated Press that North Korea could fire more missiles in coming days, but said there was little possibility it could fire an intercontinental ballistic missile, as it threatened in April.
He spoke on condition of anonymity because he was not authorized to speak to media.
Daniel Pinkston, a Seoul-based analyst for the International Crisis Group think tank, said both political and military reasons were behind the launches.
"I think it's a demonstration of their defiance and rejection of the U.N. Security Council Resolution 1874, for one thing, and to demonstrate their military power capabilities to any potential adversaries," Pinkston said.
He also pointed out that July 4 is not only U.S. Independence Day but also the anniversary of a 1972 joint communique in which the two Koreas agreed to work toward peacefully reunifying their divided peninsula.
During the U.S. Independence Day holiday in 2006, Pyongyang fired a barrage of missiles, including a long-range Taepodong-2 that broke apart and fell into the ocean less than a minute after liftoff. Those launches, which occurred on July 5 in North Korea, also came amid tensions with the U.S. over North Korea's nuclear program.
North Korea's state news agency carried no reports on the launches. But the North had warned ships to stay away from its east coast through July 10 for military exercises - an indication it was planning launches.
The chief of U.S. Naval operations, Adm. Gary Roughead, said Saturday 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 before news of the launches.
South Korea and Japan, which are within easy range of North Korean missiles, condemned the launches as a "provocative" act that violates the U.N. resolution.
South Korea "expressed deep regret over the North's continuous behavior that escalates tensions in Northeast Asia by repeatedly defying" the resolution, the Foreign Ministry said in a statement.
In Tokyo, Chief Cabinet Secretary Takeo Kawamura said in a statement that the launch of missiles "is a serious act of provocation against the security of neighboring countries, including Japan, and is against the resolution of the U.N Security Council."
In Beijing, a Foreign Ministry spokesman said he had no immediate comment. China is the North's closest ally.