"First, we need to transition from a bilateral dialogue on nuclear nonproliferation to a multilateral dialogue," Cartwright said at a roundtable on the normalization of Russia-US relations in Moscow.
The New Strategic Arms Reduction Treaty (New START) was enacted in 2011 to reduce the total number of deployed US and Russian nuclear warheads to 1,550 and heavy bombers, equipped with nuclear warheads, to 700 by February 2018.
New START requires 18 annual on-site weapons inspections and information exchanges on the number of armaments every six months.
Cartwright called for the two leading nuclear powers to "not stop on the goal of reductions" and continue toward further non-proliferation.
"We need that dialogue restarted," he reaffirmed.
Cartwright serves as the inaugural Harold Brown Chair in Defense Policy Studies at the Center for Strategic and International Studies think tank. He chairs the Global Zero nuclear weapons elimination campaign.