North Korean leader Kim Jong Un said cooperation between his country and Russia has been "strengthened as never before" in a message sent Friday to celebrate Russian President Vladimir Putin's 70th birthday, state-run media said.

In the message, Kim said he has "rejoiced" in the strengthened mutual support and cooperation enabled through the struggle "to defend the regional peace and stability and justice," according to the official Korean Central News Agency.

"Today, Russia is reliably defending the dignity of the state and its fundamental interests from the challenges and threats by the U.S. and its vassal forces. Such reality is unthinkable without your distinguished leadership and strong will," KCNA quoted Kim as telling Putin.

"I wish you happiness in good health and great success in your responsible work for the prosperity of Russia," he said.

North Korea said Tuesday it supports Moscow's annexation of four occupied Ukrainian regions, according to KCNA, following Pyongyang's recognition of Russia-backed separatist regions in the war-torn nation's east as independent states in July.

At an emergency meeting of the U.N. Security Council on Wednesday, Russia defended North Korea's ballistic missile launch over the Japanese archipelago the previous day, labeling it a response to a recent joint military drill conducted by the United States, South Korea and Japan.

North Korea, founded in 1948 with the backing of Russia's predecessor state the Soviet Union, has been trying to deepen ties with Russia and China, as the nation's negotiations with the United States over denuclearization and sanctions relief have been in a stalemate for around three years.