Russian President Vladimir Putin and North Korean Leader Kim Jong Un have signed an agreement pledging they will come to each other’s aid if either is faced with “aggression” from any adversary.

While the details are not fully known, both leaders agreed that the pact is one of the strongest they have had since Putin’s last visit to North Korea in 2000. The agreement emerged after one-on-one talks lasting approximately 90 minutes. 

According to a report from Russian news agency Sputnik, putin said “A new fundamental document was prepared today, something that will form the basis of the long-term relationship between Moscow and Pyongyang.”

White House National Security Communications Adviser John Kirby said the Biden administration was “not concerned about the trip. What we are concerned about is the deepening relationship between the two countries.”

U.S. officials further noted that North Korea may be supplying the Russian military with ballistic missiles and other munitions to use in the war against Ukraine, in exchange for economic assistance and technology transfers.

North Korea previously had a treaty with the former That alliance, according to the treaty document, was “based on the principle of socialist internationalism” and to “promote the maintenance and strengthening of peace and security in the Far East and throughout the world in accordance with the purposes and principles of the United Nations.”

However, Eurasia Group founder and President Ian Bremmer that Russia’s new agreement with North Korea should be concerning for everyone.

“The Russians cannot get military equipment directly from countries that are concerned about facing American, European, Japanese and South Korea sanctions, so that doesn’t leave many countries out there willing and capable to help Russia with their war effort,” Bremmer said. He added that Russia has thus been forced to partner with countries that are considered “rogue,” like Iran and North Korea, and that they have the economic means to get what they want.

“The fact that this country is now working so closely with a chaos actor like North Korea, that we have no influence over, we have very little intelligence about, we have no engagement with, should be a serious concern for pretty much everyone out there,” Bremmer said.

Putin has reportedly now flown to Vietnam to reinforce between the two countries.