WASHINGTON : US Secretary of State Rex Tillerson Sunday denied that Donald Trump's threat to tear up the Iran nuclear deal had weakened America's chance of reining in North Korea through diplomacy.

Asserting that Washington had "unified the international community" on the North Korean threat, Tillerson vowed efforts to contain its nuclear and ballistic missile drive through diplomacy would continue "until the first bomb drops." In a virulent speech watched around the world Friday, Trump refused to certify Iran's compliance with the 2015 deal on curbing its nuclear program, kicking the accord's fate to Congress.

By calling into question the landmark deal -- worried allies fear the US president sent a message to Pyongyang that America's word cannot be trusted. Tillerson pushed back at that notion on CNN's State of the Union, saying: "I think what North Korea should take away from this decision is that the US will expect a very demanding agreement with North Korea."

"One that is very binding and achieves the objectives not just of the United States but the policy objectives of China and other neighbors in the region, a denuclearized Korean peninsula. If we achieve that, there will be nothing to walk away from because the objective will be achieved."

The US ambassador to the United Nations Nikki Haley pushed the same argument during appearances on Sunday talk shows, telling ABC's This Week that reevaluating the Iran deal "sends the perfect message to North Korea, which is, we're not going to engage in a bad deal."