North Korea says the tests are meant to deter enemy attackers. There have been six projectiles in all. They all followed a similar trajectory into the sea.
Officials are looking into whether the projectiles were missiles or rockets fired from a large-caliber gun North Korea could have in the works.
North Korea regularly conducts short-range missile tests. According to analysts, the recent launches could be an attempt to get U.S. and South Korean attention amid tentative signs of diplomacy after soaring tensions that followed U.N. sanctions aimed at a North Korean nuclear test in February.
Pentagon press secretary George Little said the Obama administration does not view the launches as a sign of renewed tensions.
"These short-range missile launches do not necessarily violate their international obligations," unlike the North's recent nuclear test and long-range rocket launch, he said.
South Korea and the United States do not believe North Korea has the technology to make nuclear warheads capable of reaching the U.S.
The Associated Press contributed to this report.