In response to recent allegations from a UN Panel of Experts that entities in Russia were procuring items for North Korea's missile program, Russia denied any knowledge or information on transactions
"I am firmly convinced that the friendship and solidarity ... will be further developed into a long-standing strategic relationship in conformity with the demand of the new era," Kim wrote.
The monitors, who report to the council twice a year, have previously accused North Korea of using cyberattacks to help fund its nuclear and missile programs.
Russian defense minister Sergei Shoigu was joined by Chinese Communist Party Politburo member Li Hongzhong at the 70th anniversary of North Korea's founding.
The 15-member Security Council met after North Korea said it tested its latest weapon on Wednesday, and claimed the weapon is the core of its nuclear strike force.
South Korea's new unification minister advocates for his ministry to be harder on the north.
The lawmaker said Kim was believed to be suffering from a "severe" sleeping disorder, citing an intelligence report.
Leader Kim Jong Un guided the test, and warned it would make enemies "experience a clearer security crisis, and constantly strike extreme uneasiness and horror into them."
In the exercises, a ballistic missile equipped with a mock nuclear warhead flew 800 km (497 miles) before hitting a target under the scenario of a tactical nuclear attack.
The sister of North Korean Supreme Leader, Kim Jong Un, warned that if the US interfered with North Korea's missile tests, it would be taken as a 'declaration of war.'