Ambassador Sin Hong-chol's comments come after senior North Korean leaders warned this week that South Korea and the United States would face repercussions for their decision to go ahead with annual joint military drills.
The drills are a "rehearsal for war" and prove the United States is responsible for destabilising the situation, he told TASS in an interview published on Wednesday.
"We will also boost cooperation between North Korea and Russia with the view to counter the US, a common threat," Sin told TASS.
Around 28,500 American troops are stationed in South Korea as a legacy of the 1950-1953 Korean War, which left the peninsula in a technical state of war when fighting ended with an armistice rather than a peace agreement.
Washington and Seoul say the joint drills are defensive in nature.