In a rare interview with Margaret Brennan of CBS News’ 60 Minutes, Secretary of State Rex Tillerson said he has been working to convince China that North Korea is a “serious threat” to its interests.

Tillerson said the threat posed to the United States by the North Korean regime is “not acceptable.” He stressed to both his 60 Minutes interviewer and the Chinese that military options remain on the table if diplomacy fails.

“I say to my Chinese counterpart, ‘You and I fail, these people get to fight. That’s not what we want,’” Tillerson told Brennan, referring to the military forces of what could ultimately include every nation in the region.

Tillerson said North Korea simply is not ready for serious diplomacy yet, so heavy sanctions pressure must be maintained. “Every month there are new sanctions rolled out. The world wants North Korea to change,” he said.

“We’re not using a carrot to convince them to talk. We’re using large sticks, and that is what they need to understand,” said Tillerson. “The pressure campaign is having its bite on North Korea, its revenue streams. It’s having a bite on its military programs.”

Tillerson made it plain the ball is in North Korea’s court, and he would settle for nothing less than an explicit request for serious negotiations to begin, rather than vague signals and public relations campaigns like Pyongyang waged at the Winter Olympics.

“I’m not sending a lot of messages back because there’s nothing to say to them at this point,” he said. “I’m listening for you to tell me you’re ready to talk.”

When Brennan asked if China was fully on board with the sanctions program, Tillerson said the U.S. has reached “a common understanding with China” that North Korea represents a “serious threat” to them as well.

“We’ve been very clear with them that they are going to have an important role to play once we get to the negotiating table,” he said of China’s role.

Tillerson declined to establish a firm timetable for negotiations, conceding that “we don’t know precisely how much time is left on the clock” before North Korea takes some action that will force the United States to respond.

“I’m going to use all the time available to me. Our diplomatic efforts will continue until that first bomb drops. My job is to never have a reason for the first bomb to drop,” he said.

South Korean President Moon Jae-in seemed to address concerns that North Korea’s Olympic charm offensive would fracture international solidarity against Pyongyang, saying on Saturday that he was not prepared to commit to North Korea’s offer of a summit meeting with South Korea alone.

“There are high hopes for a North-South summit but I think it is a bit rushed,” said Moon. “We have a Korean saying, which is ‘looking for hot water beside the well.’”

“The general consensus on the need for dialogue between the U.S. and North Korea is gradually increasing. We are waiting for the current inter-Korean talks to lead to dialogue between the U.S. and North Korea, and to denuclearization,” the South Korean president added, reading from the same playbook as Secretary of State Tillerson.

According to Nikkei Asian Review (NAR), Chinese President Xi Jinping also had no particular interest in North Korea’s Olympic diplomacy. Instead, China is primarily concerned with determining if the U.S. is truly serious about taking military action against North Korea if Pyongyang refuses to negotiate on nuclear disarmament.

“Xi ignored the Pyeongchang Olympics and had eyes on Donald Trump alone. That’s clear from China’s diplomatic actions on the day of the opening ceremony,” a Chinese source said.

Nikkei Asian Review talks at length about tensions between Beijing and Pyongyang, which seem to include some degree of personal animosity between Xi and North Korean dictator Kim Jong-un, as well as China’s sense that the North Korean crisis is compromising its military and economic interests.

The former includes China’s dismay over South Korea deploying the American THAAD anti-missile system and its powerful radars, while the latter includes both Chinese losses due to sanctions against North Korea and Chinese boycotts imposed during feuds with South Korea. It is possible that even if Secretary of State Tillerson has not quite convinced the Chinese to view North Korea as an outright threat, they are beginning to see their hideous client state as a liability, which could be almost as useful.

One interesting signal of Chinese displeasure mentioned in the NAR article is that Chinese media downplayed North Korea’s offer of a bilateral summit between Kim and Moon. China previously advocated for such a summit, but treated Pyongyang’s offer as news scarcely worth mentioning.