Top US Envoy Begins Asia Tour amid North Korea Crisis

US Secretary of State Rex Tillerson has promised to take a tough line on Kim Jong-un's isolated regime as he talks to allies Japan and South Korea and to rival great power China.

The former oilman will also talk commerce, after President Donald Trump's belligerent campaign rhetoric raised the specter of a trade war between the United State and China.

But US officials confirmed North Korea's provocative behavior would be "front and center" as Tillerson meets Japan's Prime Minister Shinzo Abe and Foreign Minister Fumio Kishida Thursday.

After Tokyo, it will be on to Seoul, a city already within range of North Korea's artillery and rocket batteries, for talks with the acting leader after a corruption scandal saw President Park Geun-Hye ousted last week.

And then at the weekend, there will be his much anticipated trip to Beijing, amid reports that Tillerson will seek to finalize plans for Chinese leader Xi Jinping to visit Trump in April.

Here, he might get a positive response. In a news conference after the annual National People's Congress parliament meeting Wednesday, Premier Li Keqiang said "there are bright prospects for China-US cooperation."

He warned that US investments in China would bear the brunt of any trade war, and argued: "I believe whatever differences we have, we can still sit down and talk to each other and work together to find solutions."

But Tillerson will also have to broach the topic of North Korea's progress towards building an intercontinental ballistic missile (ICBM) that would be able to threaten US mainland cities or bases in the Pacific.

"He's going to have an opportunity at every stop to talk about next steps or what we do now, with respect to North Korea," acting State Department spokesman Mark Toner told reporters.

"I mean, it's obviously the looming challenge over our relations and, frankly, the security of the Korean Peninsula," he added in a news briefing before Tillerson left Washington.

China is perhaps the last country with significant leverage over North Korea, which has ignored several rounds of UN-backed sanctions targeting its banned nuclear weapons program.

Beijing shares US concerns over Pyongyang's attempts to build an arsenal of nuclear devices, but has been much more measured in its reaction to the ballistic missile program.

Xi's government has been reluctant to back any moves that might destabilize Kim's regime, and is publicly more concerned about Washington's decision to deploy the THAAD missile defense program in South Korea.

Washington insists THAAD is a defensive system deployed to protect the South and U.S. bases from North Korean missiles, but China fears its advanced radar system undermines China's nuclear deterrent.

In recent comments, China's Foreign Minister Wang Yi implied the United States and North Korea were equally at fault for the latest crisis and moving towards a "head-on collision".

With apparently little prospect of a breakthrough, some foreign policy hawks in Washington have been pushing for secondary sanctions that would hurt Chinese banks doing business with North Korea.

But US officials played down expectations of any announcement during the trip, AFP reported.

Instead, Tillerson will test Chinese receptiveness to the idea of tougher measures on North Korea, while attempting to calm fears of an imminent trade dispute between the world's two largest economies.

"Everybody agrees on the challenge, which is: How do you stop North Korea's bad behavior?" Toner said. "I think part of this trip will be about trying to hone in on some next steps.

"I think he really wants to try to drill down on that challenge for this trip. But let's not also ignore the other 800-pound gorilla in the room here, which is our trade relations with the region. It's hugely important."