Despite his concerns about Russia and China and the "unraveling" of the international arms controls regimes the world has long depended on, the NATO chief emphasized the need to negotiate new arms control arrangements.
After four weeks, a crucial session to shore up the world's nuclear arms control regime ended without agreement when Russia rejected a reference to Ukraine.
He had been in poor health since 2018 and already let it be known he planned to resign next March, midway through his third term, which would have run through 2021.
Two nuclear watchdogs, the IAEA and CTBTO, declared themselves prepared to carry out the monitoring and verification North Korea would need for denuclearization.
Diplomats registered protest, outrage and regret that Syrian President Bashar Assad's government would preside over the forum, saying it has no credibility or moral authority.
The U.N. secretary-general launched a campaign underscoring the need for nations to scrap nuclear arsenals and other weapons that could result in catastrophic mistakes.