U.S. relations with North Korea are about to enter a new phase, as Secretary of State Rex Tillerson told a news conference in Seoul that the policy of "strategic patience" with North Korea is ending and that the U.S. is exploring "a new range of security and diplomatic measures" where "nothing [is] off the table" – including military force.

Tillerson made the remarks at the start of his first trip to Asia, which will include stops in South Korea, Japan, and China.

Reuters:

He said any North Korean actions that threatened the South would be met with "an appropriate response".

"If they elevate the threat of their weapons program to a level that we believe requires action, that option is on the table," Tillerson said when asked about military action.

Tillerson also called on China to implement sanctions against North Korea and said there was no need for China to punish South Korea for deploying an advanced U.S. anti-missile system aimed at defending against North Korea.

China says the Terminal High Altitude Area Defense (THAAD) system's powerful radar is a threat to its security.

"We believe these actions are unnecessary and troubling," Tillerson said, referring to what South Korea sees as Chinese retaliation in the form of business restrictions in response to the deployment of the missile system.

"We also believe it is not the way for a regional power to help resolve what is a serious threat for everyone. So we hope China will alter its position on punishing South Korea."

"We hope they will work with us to eliminate the reason THAAD is required."

North Korea has conducted two nuclear tests and a series of missile launches since the beginning of last year.

Last week, it launched four more ballistic missiles and is working to develop nuclear-tipped missiles that can reach the United States.

South Korean Foreign Minister Yun Byung-se told the joint news conference the missile system was only intended to defend against North Korea, not any other country.

The idea of "strategic patience" is shorthand for "do nothing and hope for the best."  The sanctions leveled against North Korea have had zero effect on the nation's progress toward building a reliable nuclear arsenal and ballistic missiles that are nuclear-capable.  The question now becomes what other actions the U.S. can take to address the clear and present danger of the North Korean nuclear threat against South Korea and Japan.

Experts don't think the North has mastered the art of being able to marry a nuclear warhead with a ballistic missile.  But how long will it be before they do?  While China has proved reluctant in the past to punish its neighbor for their illegal activities, the Chinese government recently banned purchases of coal from North Korea for the rest of the year.  This will have an impact on the already teetering North Korean economy.  Despite that, the North has shown no softening of its position that it has the absolute right to build nuclear weapons.  And to make matters worse, the nation has ratcheted up its bloodthirsty threats against the U.S. and the South, promising a nuclear war if it thinks it becomes necessary.

No doubt, North Korea will be the number-one topic of conversation between Tillerson and his counterparts in the Far East.

The latest bout of tension with North Korea comes at a time of political turmoil in South Korea. President Park Geun-hye was ousted last week after being impeached in a corruption scandal and an election for a new president will be on May 9.

A liberal opposition politician, Moon Jae-in, who has raised questions about the THAAD deployment, is leading in the opinion polls.

Tillerson, a former oil executive with no prior diplomatic experience, said he expected a new government would "continue to be supportive" of the deployment, adding it was also intended to protect U.S. troops in South Korea.

China resents U.S. pressure to do more on North Korea and says it is doing all it can but will not take steps to threatened the livelihoods of the North Korean people.

China has urged North Korea to stop its nuclear and missile tests and said South Korea and the United States should stop joint military exercises and seek talks instead.

Chinese Foreign Ministry spokeswoman Hua Chunying reiterated that talks were the best way to resolve the problems of the Korean peninsula.

"As a close neighbor of the peninsula, China has even more reason than any other country to care about the situation," she told a briefing.

Hua also said the THAAD would "upset the regional strategic balance". Its radar, with a range of more than 2,000 km (1,250 miles), meant it could cover a large part of China, far outside the scope of the threat South Korea faces, Hua said.

Tillerson is hopeful that a new South Korean government will continue the THAAD deployment, but in the face of Chinese pressure, the new South Korean government – to be elected in about two months – might easily give in.  The deployment, as noted above, is a source of friction between the U.S. and China, and President Xi may be seeking some additional assurances from Tillerson when they meet next week.

How likely is war between the U.S. and North Korea?  I think the end of the strategic patience policy is a signal to Kim Jong-un that the North's developing nuclear threat against U.S. allies in the region will not be allowed to materialize.  The U.S. and Japan will not tolerate an operational North Korean nuclear ballistic missile system – not when any test of a North Korean missile might be misconstrued in Seoul and Tokyo as the real thing. 

China also recognizes the destabilizing nature of the North Korean nuclear and ballistic missile program.  But can Secretary Tillerson convince the Chinese to exert their considerable influence on the North to prevent a war?