North Korea has derided South Korean President Yoon Suk Yeol as “a guy with a trash-like brain” and “a diplomatic idiot” as it blasted him for using a UN speech to issue a warning over the North’s deepening military ties with Russia.

In a speech at the UN General Assembly last week, Yoon said South Korea “will not sit idly by” if North Korea and Russia agree to weapons deals that would pose a threat to the South.

North Korean leader Kim Jong Un’s trip to Russia earlier this month to meet President Vladimir Putin and visit key military sites raised international concern about a possible push by North Korea to receive sophisticated nuclear and weapons technologies in return for replenishing Russia’s conventional arms inventory depleted by its war with Ukraine.

“Puppet traitor Yoon Suk Yeol, even at the 78th UN General Assembly, malignantly slandered the relations between (North Korea) and Russia,” the North’s official Korean Central News Agency said in a commentary.

Without addressing the worries about a possible weapons deal with Russia, KCNA said it’s “quite natural” and a “legitimate right” for neighbouring countries to keep close ties with each other.

“It’s self-evident that such a guy with a trash-like brain cannot understand the profound and enormous meaning of the development of (North Korea)-Russia friendly relations,” KCNA said.

Koo Byoungsam, a spokesperson for South Korea’s Unification Ministry, said the insults demonstrated North Korea’s “substandard system that lacks basic etiquette and common sense.”

Since taking office last year, Yoon, a conservative former prosecutor, has sought to strengthen South Korea’s military alliance with the United States, drawing an angry response from North Korea. Monday’s KCNA dispatch accused Yoon of “voluntarily acting as a servile trumpeter and loudspeaker for the US”

Also Monday, the South Korean and US navies began three days of joint naval drills off the Korean Peninsula’s east coast to improve their joint operational capability. North Korea views South Korean-US military exercises as invasion rehearsals and typically reacts with its own missile tests.

The US and South Korea have warned that Russia and North Korea will face undefined consequences if they enter into weapons transfer deals in violation of UN Security Council resolutions that ban any weapons trade with North Korea. Russia, a permanent member of the Council, endorsed those UN resolutions.

In his UN speech, Yoon said “It is paradoxical that a permanent member of the UN Security Council, entrusted as the ultimate guardian of world peace, would wage war by invading another sovereign nation and receive arms and ammunition from a regime that blatantly violates Security Council resolutions.”

North Korea is notorious for using crude invectives against South Korean and US leaders. It called previous South Korean Presidents Lee Myung-bak and Park Geun-hye “a rat” and “a prostitute” respectively. It described former US President Donald Trump as “a mentally deranged US dotard” and called Barack Obama a monkey.