Russian President Vladimir Putin has ordered his top officials to draft plans for a possible nuclear test, something Moscow has not done since the collapse of the Soviet Union in 1991.

The order comes after US President Donald Trump's announcement last week that the United States will also resume testing.

• Guest: Jeffrey Lewis, Professor at the James Martin Centre for Non-proliferation Studies at the Middlebury Institute of International Studies, in California. Also hosts "Arms Control Wonk" podcast
• Producer: Anne Barker