North Korea fired five short-range ballistic missiles into the Sea of Japan Monday, the Pentagon confirmed Monday. 

"Launches using ballistic missile technology are a clear violation of multiple UN Security Council resolutions. We call on North Korea to refrain from actions that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its international commitments and obligations," Pentagon spokesman Bill Urban said.

The launches were first reported by the Yonhap News Agency. South Korea's Joint Chiefs of Staff reported that the missiles were launched from the city of Hamhung, in northeastern North Korea, and traveled approximately 125 miles before landing in the water.

Earlier Monday, Yonhap reported that the South Korean government had warned that North Korea was capable of conducting a fifth nuclear test at any time.

The latest launches appeared to be part of North Korea's response to ongoing South Korea-U.S. military drills it sees as a provocation and a rehearsal for an invasion. In the past two weeks North Korea has fired several short-range missiles and artillery shells into the sea and threatened pre-emptive nuclear strikes against Washington and Seoul.

This year's drills are the largest ever, and come after the North's nuclear test and long-range rocket launch earlier this year.

The U.S. special representative for North Korean policy, Sung Kim, who is visiting Seoul, said Monday that North Korea "should refrain from all provocative actions, including missile tests, which are clearly in violation of Security Council resolutions."

On Sunday, North Korean state TV broadcast photos showing leader Kim Jong Un supervising landing and defensive drills. The photos showed artillery blazing, navy ships landing as shells fell nearby, and soldiers running with the national flag. North Korea has a history of photo manipulation and there was no way to verify the authenticity of the photos.

On Friday, North Korea claimed that it had launched two medium-range ballistic missiles capable of striking Japan, the first such launches since 2014. However, U.S. officials later told Fox News that one of the missiles blew up shortly after lift-off. Despite that embarrassment, the fact that the other missile traveled hundreds of miles marked a dangerous escalation of North Korea's missile program.

Last week, President Obama signed new sanctions targeting North Korea's coal industry, which some analysts suspect fuels its missile program. An earlier sanctions bill signed by Obama targeted luxury goods consumed by North Korea's elite.

Also last week, North Korea sentenced a 21-year old American college student from the University of Virginia to 15 years of hard labor in a prison camp for allegedly stealing a banner while in the communist country.

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.