A new agreement between Russian President Vladimir Putin and North Korean leader Kim Jong Un requires both the countries to provide each other with immediate military assistance in case of a war, North Korea's state media said.

The Korean Central News Agency (KCNA) on Thursday said that the language of the comprehensive strategic partnership agreement was agreed upon by both Putin and Kim Jong Un in Pyongyang on Wednesday.

Article of 4 of the agreement reads that if one of the countries is invaded and comes under a state of war, the other must deploy "all means at its disposal without delay" to provide "military and other assistance".

This deal could be the strongest connection between Pyongyang and Moscow since the end of Cold War. Putin and Kim described the event to be a major development in their relations, including security, trade, investment, cultural and humanitarian ties.

The summit came in the backdrop of growing concerns of the United States and its allies that a possible arms deal in which Pyongyang would provide badly needed munitions to Moscow for it war in Ukraine, in return for economic and technological assistance that could further enhance the threat from Kim's nuclear weapons and missile programme.

After their meeting, Kim said North Korea and Russia had a "fiery friendship", adding that the deal was their "strongest-ever treaty", taking their relationship to the level of an alliance.

The North Korean leader vowed full support to Russia in its war in Ukraine. Meanwhile, Putin called it to be a "breakthrough document" which reflected the mutual desires of the two nations to take their relations to higher levels.

Experts have said that the treaty signed between North Korea and the former Soviet Union in 1961 necessitated Moscow's military intervention if North Korea ever came under attack. However, this deal was cancelled after the collapse of USSR. It was replaced by another agreement in 2000 but that offered weaker security assurances.

Notably, officials in South Korea said that they were assessing the outcomes of the summit between the two leaders, wondering how Russia would react if the North came under attack and whether the assistance provided will be of the same level as that promised in the 1961 treaty.

With the pace of Kim's weapons testing and the US-South Korea-Japan combined military exercises intensifying in what is said to be a tit-for-tat cycle, tensions on the Korean Peninsula appear to be at their highest level in years.

Both the Koreas have been engaged in a Cold War-fashioned psychological warfare, with North Korea dropping tons trash balloons on the South and the latter broadcasting anti-North Korean propaganda on loud speakers.

The North Korean state media, KCNA, on Thursday released the full text of the agreement between the two nations, which also spelled cooperation on nuclear energy, space exploration and food and energy security, Reuters reported.

Citing the agreement, KCNA also reported that Russia and North Korea will not sign any treaty with a third country that violates the interests of the other, not allowing any other country to use their territory to harm the other's security and sovereignty.

At the summit, Putin thanked Kim for North Korea's support to his nation in Ukraine, part of which he said was a "“fight against the imperialist hegemonistic policies of the US and its satellites against the Russian Federation.”

US Secretary of State Antony Blinken, meanwhile, said Putin's visit to North Korea illustrates how Russia is trying in "desperation, to develop and to strengthen relations with countries that can provide it with what it needs to continue the war of aggression that it started against Ukraine".

(with agency inputs)