A former U.S. State Department official said that a meeting between U.S. President Donald Trump and North Korean leader Kim Jong-un would require Russia's cooperation.

At an event hosted by Georgetown University's SFS Korea Policy Club on Tuesday, Mark Lambert, former deputy assistant secretary in East Asia and Pacific affairs, predicted that the "bromance" between the leaders of China and Russia would complicate matters.

Lambert said Pyongyang appears uninterested in resuming dialogue with Washington and is more focused on its ties with Moscow.

The former official said China would need to consult with Russia if it were to mediate a meeting between Trump and Kim, and that it remains uncertain whether Moscow would cooperate.

Lambert, who handled denuclearization talks with the North during Trump's first term, said he disagrees with former U.S. Secretary of State Mike Pompeo's recent comment that there are currently "no carrots" and a low number of "sticks" to convince the regime to give up its nuclear program.

The former official said he is convinced that the U.S. managed to tame the North with "sticks" and that Kim, during Trump's first term, showed great interest in the regime's economic development.