Russia has allowed the release of millions of dollars in frozen North Korean assets and may be helping its isolated ally with access to international banking networks, assistance that has come after the North’s transfer of weapons to Moscow for use against Ukraine, according to American-allied intelligence officials.

The White House said last month that it had evidence that North Korea had provided ballistic missiles to Russia, and that the North was seeking military hardware in return. North Korea also appears to have shipped up to 2.5 million rounds of ammunition, according to an analysis by a British security think tank.

While it is unclear whether Russia has given North Korea the military technology it may want, new banking ties would be another sign of the steady advancement in relations between the countries. The expanding partnership has most likely emboldened the North, as it has issued a stream of belligerent threats in recent months, U.S. officials say.