North Korea has fired two medium-range Rondog missiles into the Sea of Japan, also known as the East Sea in Korea.
The U.S. State Department said the missiles were fired early Wednesday. South Korea's Yonhap news agency said the missiles have a range of about 1,300 kilometers. The report said the missiles flew about 450 kilometers.
The State Department said the launches are "a troubling and provocative escalation" and "a clear violation of U.N. Security Council resolutions" that require North Korea to suspend all activities related to its ballistic missile program and to re-establish a moratorium on missile launches. The U.S. statement said there was no warning before the launches.
The launch came as leaders of the United States, Japan and South Korea met in the Netherlands, with North Korea's nuclear ambitions high on the agenda of their talks.
Before the meeting started Tuesday, U.S. President Barack Obama said deepening coordination among Washington, Tokyo and Seoul, including "military cooperation that includes joint exercises," is vital to dealing with North Korea.
The latest launches -- following a recent series of short-range rocket launches -- could be a North Korean response to the trilateral summit.
Pyongyang fired 16 short-range rockets into its eastern waters early Sunday, following similar launches of 30 rockets Saturday.
Analysts say the launches are an expression of Pyongyang's anger at ongoing annual South Korean - U.S. military drills, which run until next month.
The North routinely criticizes the drills, saying they are rehearsals for an invasion.