The United Nations Security Council will meet Tuesday to discuss the latest missiles launched by North Korea, diplomats say.
The North fired three ballistic missiles into the Sea of Japan on Monday from a site in Hwanghae province, located on the country's eastern coast.
South Korea's Joint Chiefs of Staffs have identified them as Rodong missiles, which have a range of 1,000 kilometers.
Japan's Defense Ministry says the rockets fell into its Exclusive Economic Zone in the region, which is known in Korea as the East Sea.
The U.S. State Department said North Korea's missile launches have become too common in the past several months.
North Korea has conducted a series of missile tests this year in defiance of U.N. sanctions imposed after its fourth nuclear test in January.
Monday's missile firings came as world leaders met in the eastern Chinese city of Hangzhou for the now-concluded two-day G-20 summit of advanced and emerging economies.
"This launch is a clear act of provocation not only to our country, but to the international community considering the timing of its launch coinciding with the G-20 summit held in China's Guangzhou today," said Japanese cabinet secretary Yoshihide Suga.
A U.S. official who attended the summit condemned North Korea's actions, calling the missile launches a threat to both aircraft and maritime vessels operating in the region.
South Korean President Park Geun-hye and Chinese President Xi Jinping met on the sidelines of the summit just hours before the missile launches.
According to Yonhap News Agency, Park warned the Chinese leader that Pyongyang's increasing provocations, including a series of nuclear weapons and ballistic missile tests, have "seriously undermined peace in this region and posed a challenge" to Seoul-Beijing relations.
Meanwhile, China's Xinhua news agency says Xi told his South Korean counterpart that Beijing opposes deployment of the U.S.-built THAAD — or Terminal High Altitude Area Defense — anti-missile system in South Korea. Seoul says the THAAD system is aimed at countering possible missile attacks from North Korea.