US President Donald Trump and North Korean leader Kim Jong-un at the 2019 North Korea-United States Summit in Hanoi (Photo: AFP)

David Stilwell, US Assistant Secretary of State for East Asia and Pacific Affairs, said the Trump administration has gone further than any previous administration to let North Korea know it is going to have to negotiate.

North Korea is trying to expand its ICBM capabilities, maybe even move to a submarine-launched ballistic missile, according to Rob Soofer, US Deputy Assistant Secretary of Defense for Nuclear and Missile Defense Policy.

At a webinar hosted by the Mitchell Institute for Aerospace Studies, Soofer said the US is beefing up its missile defense capabilities in response.