Rex Tillerson: Pre-emptive military action against North Korea is an option

"The policy of strategic patience has ended," the secretary of state said.

"All of the options are on the table," Tillerson said when asked at a press conference Friday with South Korean foreign minister Yun Byung-se in Seoul whether he would rule out military conflict against North Korea.

His comments came after a visit to the militarized border between South Korea and North Korea and a day before the U.S. secretary of state is to arrive in Beijing for meetings with Chinese officials.

As if to underline Tillerson's remarks, President Trump later on Friday tweeted that "North Korea is behaving very badly" and that "China has done little to help."

Referring to how the Obama administration hoped sanctions would cripple North Korea to the point where it would renew de-nuclearization negotiations, Tillerson added, "Let me be very clear: the policy of strategic patience has ended."

He also emphasized that the U.S. had no plans to curtail its military activities in the region.

"We don't believe conditions are right for talks and we have no intention of ending military exercises," he said.

The Associated Press contributed to this report.