Moscow is trying to explain to Pjongjang that its nuclear mad talk is counter-productive to its security
Firstly the Russians note that the current US-South Korean war games are indeed an annual event, but also points out that crucially the games which involve involving 300,000 South Korean and 17,000 American troops are massive and the largest such event yet:
"On March 7, the United States and South Korea started military exercises, which are formally considered to be planned but in reality are unprecedented in their scale and the number and types of weapons used as well as the type of maneuvers drilled," the Russian Foreign Ministry went on to say.
As such the Russians can't help but sympathise with the North Koreans and take their concerns about their historic superpower tormentor playing wargames on their borders as legitimate:
"Naturally, as a state, which is directly named as an object of this kind of military activities, the Democratic People’s Republic of Korea (DPRK) cannot but feel reasonably concerned for its security. Russia has many times stated its openly negative attitude to such manifestations of military and political pressure on Pyongyang," the Russian Foreign Ministry said.
However, the Russians have no sympathy for the North Korean reaction of threatening to deliver a "preventive and offensive nuclear strike" against the exercise and are speaking out against it harshly:
"We consider it to be absolutely impermissible to make public statements containing threats to deliver some ‘preventive nuclear strikes’ against opponents," the Russian Foreign Ministry stressed.
Crucially the Russians want Pjongjang to understand that such threats only serve to isolate it and make the invasion it fears more, rather than less, likely:
Pyongyang should be aware of the fact that in this way the DPRK will become fully opposed to the international community and will create international legal grounds for using military force against itself in accordance with the right of a state to self-defense enshrined in the United Nations Charter.
In other words. If Pyongyang persists with mad talk it makes it impossible for Russia to offer diplomatic support when its enemies take aim against it.