US President Barack Obama on Sunday accused North Korea of "provocation" following reports of renewed missile testing by the isolated country.
While the United States lacked precise information on the latest tests, they were being "taken very seriously," Obama said in the German city of Hanover following talks with Chancellor Angela Merkel.
"What is clear is that North Korea continues to engage in continuous provocative behavior, that they have been actively pursuing a nuclear programme, an ability to launch nuclear weapons," he said.
"And although more often than not they fail in many of these tests, they gain knowledge each time they engage in these tests," Obama said.
On Saturday, North Korea fired what was believed to be a submarine-launched ballistic missile (SLBM) in the Sea of Japan. Supreme Leader Kim Jong Un gave the order for it to be fired, the North's KCNA news agency reported, calling the test a success.
South Korea said the launch failed because the missile only flew for about 30 kilometres, whereas the minimum range for an SLBM is 300 kilometres, Yonhap news agency reported.
Obama called on China, North Korea's neighbour, to apply pressure on Pyongyang to halt the tests and said the US aimed to ensure the security of its allies in the region, South Korea and Japan.
"What is clear is that North Korea is continuing to engage in provocative behavior," Obama said. "If North Korea shows seriousness in denuclearizing the Korean peninsula, then we will be ready to engage in serious conversations with them to reduce tensions."
The UN Security Council issued a statement Sunday strongly condemning the firing of the ballistic missile.
"This incident constituted yet another serious violation by [North Korea] of United Nations Security Council resolutions," the statement said, citing five resolutions passed in 2006, 2009, 2013 and this year.
The council said North Korea's development and testing of newballistic missile capabilities were clearly prohibited by the resolutions even if launches fail.