Russian and US diplomats held talks behind closed doors in Geneva on Thursday, the latest round of discussions between the world's top two nuclear powers following a June summit between US President Joe Biden and Russian counterpart Vladimir Putin.
US State Department number two Wendy Sherman and Russia's deputy foreign minister Sergei Ryabkov were expected to meet for most of the day.
The talks began around 10:00 am (0800 GMT), said a member of Russia's mission to the UN.
State Department disarmament chief Bonnie Jenkins had earlier said that Washington hoped "concrete steps" would emerge from the talks in Geneva.
Beyond disarmament, the two sides were expected to discuss new technologies, space and artificial intelligence, Swiss news agency ATS reported.
Thursday's talks were being held at Russia's UN mission, after the last round in late July was hosted by the Americans a few hundred metres (yards) away.
Arms control was at the top of the agenda at that exchange.
At their June 16 summit, Biden and Putin said that it was vital to keep talking despite the differences that divide the two nuclear giants.
Even at the height of the Cold War, Moscow and Washington stayed in contact to prevent a conflict breaking out, they said.