Russian President Vladimir Putin, left, and North Korea's leader Kim Jong-un pose for a photo during a signing ceremony of the new partnership in Pyongyang, North Korea, June 19. AP-Yonhap

A new defense treaty signed by the leaders of North Korea and Russia in June came into force this week as the two nations have exchanged the treaty ratification instruments, state media reported Thursday.

The comprehensive strategic partnership treaty went into effect Dec. 4, when the two sides signed protocol on exchanging the ratification instruments, according to the Korean Central News Agency (KCNA).

At summit talks in Pyongyang in June, North Korean leader Kim Jong-un and Russian President Vladimir Putin signed a new defense treaty that calls for providing military assistance "without delay" if either side comes under attack.

The two nations have been deepening military cooperation, with North Korea sending thousands of troops to Russia in support of Moscow's war with Ukraine, spawning concerns about an escalation of the protracted conflict.

North Korea said the treaty serves as a "legal framework" that will help put bilateral ties on a new strategic level and firmly defend the regional and global security environment in conformity with the common interests of the two nations.

The North Korea-Russia ties based on the treaty will be a "powerful security device that promotes the wellbeing of the peoples of the two countries, eases the regional situation and guarantees international strategic stability," the KCNA said.

"It will serve as a strong driving force accelerating the establishment of an independent and just multi-polarized world order without domination, subjugation and hegemony," it added.

Experts said the new defense treaty is seen as warranting automatic military intervention in the event of an attack on either country. That would amount to the restoration of a Cold War-era alliance for the first time since a mutual defense treaty was scrapped in 1996.

In a meeting with Russian Defense Minister Andrei Belousov last week, the North's leader Kim expressed his "invariable" support for Russia's war against Ukraine.

Observers raised the possibility of Russia asking for North Korea to further provide weapons or send troops and the North requesting rewards in return for its military support. (Yonhap)