WASHINGTON (Reuters) – Secretary of State Rex Tillerson said Sunday that President Donald Trump had instructed him to continue diplomatic efforts to calm rising tensions with North Korea, saying “those diplomatic efforts will continue until the first bomb drops.”

Speaking on CNN’s “State of the Union,” Tillerson downplayed messages that President Trump had previously posted on Twitter suggesting Tillerson was wasting his time trying to negotiate with “Little Rocket Man,” a derogatory nickname Trump has coined for North Korea’s leader Kim Jong Un.

Trump “has made it clear to me to continue my diplomatic efforts,” Tillerson said.

Tillerson’s comments Sunday come amid soaring tensions between the United States and North Korea following a series of weapons tests by Pyongyang and a war of words between the two countries’ leaders.

North Korea has conducted a series of nuclear tests in recent weeks and ago and launched two missiles over Japan.

Tillerson has been in talks with China to enlist its help on getting North Korea to back down.

But Trump’s recent Twitter messages appeared to undercut Tillerson’s efforts, prompting the Senate Foreign Relations Committee Chairman Bob Corker to complain that Trump was publicly castrating Tillerson and hurting diplomatic talks.

Tillerson downplayed those tweets Sunday, telling CNN that Trump and China’s President Xi Jinping have an extremely close relationship and that China understands the U.S. position.

“Rest assured that the Chinese are not confused in any way” about the American policy towards North Korea, he added.