The United States sanctioned top North Korean officials, including leader Kim Jong Un, on Wednesday for what it said were "notorious abuses of human rights."
North Korea fired a submarine-launched ballistic missile off its east coast, South Korea said, amid concerns that the isolated state might conduct a nuclear test or a missile launch.
North Korea fired what appeared to be a medium-range ballistic missile into the sea on Friday, just days after leader Kim Jong Un ordered further nuclear warhead and missile tests, South Korea's defence ministry said.
South Korea resumed high-decibel propaganda broadcasts into North Korea as the US ramped up pressure on China to bring Pyongyang to heel after its latest nuclear test.
South Korea is in talks with the US to deploy US strategic weapons on the Korean peninsula, a day after North Korea said it successfully tested a hydrogen nuclear device.
North Korea said it had successfully conducted a test of a miniaturised hydrogen nuclear device, marking a significant advance in the isolated state's strike capabilities and raising alarm bells in Japan and South Korea.
