North Korean leader Kim Jong Un has sent a birthday message to Russian President Vladimir Putin, calling him his “closest comrade”.

Kim, congratulating Putin on his 72nd birthday, added that relations between both countries would be raised to a new level.

Relations between Pyongyang and Moscow have deepened since the start of the Ukraine war – in a move that has worried the West.

Separately on Tuesday, Kim said Pyongyang would speed up steps to make his country a military super power with nuclear weapons.

According to Yonhap News quoting North Korean state media KCNA, Kim praised relations between both countries, saying they had become “invincible and eternal”, since Putin’s visit to Pyongyang in June.

“Meetings and comradely ties between us… will make a positive contribution to further consolidating the eternal foundation of the DPRK-Russia friendship,” he added, referring to North Korea by its official name, the Democratic People’s Republic of Korea.

Earlier this year, Putin and Kim signed an agreement pledging that they would help each other in the event of “aggression” against either country – though it was unclear what would constitute aggression.

Kim has been accused of helping Russa in the war against Ukraine by supplying it with weapons in exchange for economic and technological assistance.

There has been growing evidence that Russia has been deploying North Korean missiles in Ukraine.

Jeffrey Lewis, a director at the James Martin Center for Nonproliferation Studies, had earlier said both Kim and Putin were “trying to reduce the pain of international sanctions by creating an alternate network of friends and partners beyond the reach of US sanctions”.

During a visit by Kim to Russia in September 2023, Putin had also promised to help North Korea develop its satellites, after several failed launches by Pyongyang.

A South Korean lawmaker also seperately on Tuesday claimed that Seoul’s military had detected apparent signs that North Korea had started to build a possible nuclear-powered submarine.

Citing Korea’s intelligence agency, Rep Kang Dae-sik said construction was still in its early stages and “further confirmation is needed on whether it is nuclear powered”.