Secretary of State Rex Tillerson speaks with reporters after meeting with Libyan Prime Minister Fayez al-Sarraj in Washington, December 1, 2017.

U.S. Secretary of State Rex Tillerson offered to begin direct talks with North Korea without pre-conditions, backing away from a key U.S. demand that Pyongyang must first accept that giving up its nuclear arsenal would be part of any negotiations.

Tillerson's new diplomatic overture comes nearly two weeks after North Korea said it had successfully tested a breakthrough intercontinental ballistic missile (ICBM) that put the entire United States mainland within range of its nuclear weapons.

"Let's just meet," Tillerson said in a speech to Washington's Atlantic Council think tank on Tuesday.

The White House later issued an ambiguous statement that left unclear whether President Donald Trump — who has said Tillerson was wasting his time pursuing dialogue with North Korea — had given his approval for the speech.

"The president's views on North Korea have not changed," the White House said. "North Korea is acting in an unsafe way ... North Korea's actions are not good for anyone and certainly not good for North Korea."

In Beijing, Chinese Foreign Ministry spokesman Lu Kang said China welcomed all efforts to ease tension and promote dialogue to resolve the problem.

China hopes the United States and North Korea can meet each other halfway and take meaningful steps on dialogue and contact, he told reporters.

Ahead of Tillerson's speech, North Korean leader Kim Jong Un vowed to develop more nuclear weapons while personally decorating scientists and officials who contributed to the development of Pyongyang's most advanced ICBM, state media said on Wednesday.

Kim said on Tuesday the scientists and workers would continue manufacturing "more latest weapons and equipment" to "bolster up the nuclear force in quality and quantity," the KCNA news agency said.