Russian President Vladimir Putin's comments that Moscow may supply weapons for North Korea after signing a defense pact with Pyongyang are "incredibly concerning," US State Department spokesperson Matthew Miller said.
Putin suggested after a visit to North Korea this week that weapons supplies to the isolated nuclear-armed country would be a mirror response to the Western arming of Ukraine.
He also warned that US ally South Korea would be making "a big mistake" if it decided to supply arms to Ukraine, and that Moscow would respond to such a move in a way that would be painful for Seoul.
"It is incredibly concerning," Miller told a news briefing when asked about Putin's remarks about possible arms supplies to North Korea.
"It would destabilise the Korean Peninsula, of course, and potentially ... depending on the type of weapons they provide, might violate U.N. Security Council resolutions that Russia itself has supported."
The pact signed by Putin and North Korean leader Kim Jong Un on Wednesday commits each side to provide immediate military assistance to the other in the event of armed aggression against either one of them.
White House national security spokesperson John Kirby called it a cause of concern, but no surprise. He said Russia's need for such foreign assistance was a sign of desperation.
"We've been talking about this and warning about a burgeoning defense relationship between these two countries now for many months through a series of downgraded intelligence that we've put out there," he said.
"Obviously it's something we've taken seriously." He added.