The Russian president said Friday that his country will continue to develop its nuclear arsenal, days after signing a new mutual defense pact with Kim Jong Un.

A key U.S. ally fired warning shots Friday — live ones to repel North Korean soldiers and a diplomatic volley to counter Russian President Vladimir Putin, as tensions rise after his new mutual defense pact with Kim Jong Un.

South Korea, which has so far only provided non-lethal aid to Ukraine, said it was considering arming Kyiv in response to a newly forged alliance between Moscow and Pyongyang reminiscent of the Cold War that has alarmed officials in the West.

Putin said that doing so would be a “very big mistake.”

“If this happens, then we will also make appropriate decisions that the current leadership of South Korea would hardly like,” he said during his state visit to Vietnam on Thursday, which immediately followed the lavish Pyongyang visit. “We reserve our right to supply weapons to other regions of the world,” he added.

The Russian president’s saber-rattling continued Friday, when he said that Russia will continue to develop its nuclear arsenal as a deterrent.