For its part, North Korea denied that it sent troops to Russia. In response to South Korea's spy agency claiming 1,500 North Korean troops were sent to Russia, North Korea's UN envoy said on Monday that it was a "groundless rumor."

Russia had denied earlier claims from Ukrainian officials that North Korean troops were fighting in Ukraine, which there is no evidence of, something that's also been acknowledged by NATO.

The South China Morning Post reported that South Korean opposition lawmakers are warning against taking action related to intelligence that isn't clear. "There is nothing clear about whether the troops presumably sent by North Korea are combatants or non-combatants, or whether they are soldiers at all," two opposition lawmakers, Kim Joon-hyung of theRebuilding Korea Party (RKP) and Lee Jae-gang of the Democratic Party of Korea (DPK), said in a joint statement.