Russia and North Korea on Wednesday signed a new "comprehensive strategic partnership" as Western officials grow increasingly concerned about the implications of President Vladimir Putin's first state visit to the nuclear-armed country in 24 years.

Russian state media reported the inking of the partnership, which included a mutual defense pact, hours after Putin arrived in Pyongyang to receive a red carpet greeting from North Korean leader Kim Jong Un and a welcome ceremony attended by thousands.

The Russian president's lavish reception included praise from Kim, who expressed full support and solidarity with Moscow, including for its "special military operation" in Ukraine, according to the state-owned news agency Tass.

In reciprocation, Putin gifted Kim another new Aurus (a Russian-built limousine), an admiral's dagger and a tea set, in a move symbolic of the two country's growing ties.

Russian officials had signaled plans for the ahead of Putin's two-day trip. The new document replaces previous treaties and reportedly covers cooperation across politics, economics, culture, humanities and security.

"The comprehensive partnership agreement signed today provides, among other things, for mutual assistance in the event of aggression against one of the parties to this agreement,"

"The Russian Federation does not rule out military-technical cooperation with the Democratic People's Republic of Korea in accordance with the document," Putin added.

It comes after the official newspaper of North Korea's ruling party reported on Tuesday that Putin had promised to help develop trade with the country and help to strengthen security across Eurasia. The article added that he supports the DPRK's opposition to its "dangerous and aggressive" enemies.

Western countries — which heavily sanction both Russia and North Korea — have been closely monitoring developments of the visit and the potential ramifications for Russia's war in Ukraine and tensions on the Korean Peninsula.

NATO Secretary-General Jens Stoltenberg told a on Tuesday that Putin's trip "confirms the very close alignment between Russia and authoritarian states like North Korea," as well as China and Iran. Stoltenberg delivered the comments alongside U.S. Secretary of State Antony Blinken.

U.S. officials have asserted that Pyongyang supplied Russia with dozens of ballistic missiles and over 11,000 containers of munitions for its war in Ukraine and that Putin could use his trip to lobby for more weaponry.

"We are, of course, also concerned about the potential support that Russia provides to North Korea when it comes to supporting their missile and nuclear programs," said Stoltenberg.

Speaking to CNBC's "Squawk Box Asia" on Wednesday, Victor Cha, senior vice president of Asia and Korea chair for the Center for Strategic and International Studies, agreed that North Korean weapon supplies to Russia could be reciprocated through Kremlin support for its nuclear program.

"The question is how badly Putin feels he needs the ammunition from North Korea to survive and to win the war," said Cha. "That may lower the bar for what he's willing to give to North Korea, particularly if Kim drives a hard deal ."

Early last year, Kim of his country's nuclear arsenal and the development of more powerful intercontinental ballistic missiles, state media reported.

"The number one vendor for that [expansion] will most likely be Russia," said Cha. "For the United States, this is a real problem ... The Ukraine war is about the best thing that could have happened for Kim Jong Un."

The White House has warned that any Russian aid to North Korea's weapon programs could have repercussions for South Korea.

On Tuesday, White House spokesperson Karine Jean-Pierre told a news briefing that growing Russia-North Korea ties "should be of great concern to anyone interested in maintaining peace and stability in the Korean Peninsula."

Cha said, however, the United States may be limited in its ability to slow the flow of weapons between Russia and North Korea, without the risk of direct war.

"[The Biden administration] is giving it more public attention, but on the policy side, I don't really see any signs of what they're trying to do with regard to this," he said.