For its part, the North test-launched a ballistic missile just ahead of the Trump-Xi meeting and has been rumored to be preparing for a possible nuclear test.
Brig. Gen. Park Chul-kyun, deputy director general for worldwide policy at the South Korean ministry; Andrew Winternitz, U.S. acting deputy assistant secretary of defense for East Asia; and Koji Kano, director for defense policy at Japan's defense ministry joined the conference call.
Trump is expected to urge Xi that China be more active in using its political and economic leverage to curb North Korea's nuclear ambitions.
In February, it also simultaneously launched four ballistic missiles off its east coast, three of which landed close to Japan. Hayden, speaking about the problem the United States faces in eliciting Chinese assistance in wrangling North Korea, noted that Beijing treats the North Korean problem as a "toothache", but has so far avoided going in for a "root canal" to solve the problem, preferring painkillers.
"If we judge that they have perfected that type of delivery system, then that becomes a very serious stage of their further development", Secretary of State Rex Tillerson said Sunday on ABC's "This Week".
"It is not clear how risky this might be for the people of South Korea, but it is worrying", he told DW.
Bolstering Tillerson's words was the Pentagon's decision Saturday night to dispatch a Navy carrier strike group toward the western Pacific Ocean to provide more of a physical presence in the region.
North Korea threatened to take "necessary counteraction" against the "reckless actions".
The isolated regime conducted 24 ballistic missile tests during 2016, and experts say it could have a nuclear-tipped missile capable of reaching the US mainland within a few years.
Joint military exercises by the US and South Korea that began in March are behind the latest round of threats and provocations. As an added complication, the North has the largest per capita standing army - estimated at one million personnel - as well as stockpiles of chemical and biological weapons.
"It signals to Pyongyang that the USA has a new sheriff in town who isn't hesitant about pulling his gun from the holster", Kim said.
"I told (President Trump) that Japan is watching closely how China will cope with this North Korean issue", Abe told reporters after the 35-minute conversation. And China will either decide to help us with North Korea, or they won't.
And he is not alone in issuing such thinly veiled threats.
Tillerson said that the us would not rule out any option in response to provocations by North Korea. But this is an unhinged regime.
However, Pyongyang's response suggested the reclusive state was determined to continue with its nuclear weapons program.
The missile could cover a full range of targets in North Korea if deployed from the southeastern city of Pohang.
USA ally South Korea has lashed out at the communist nation over the launch on Wednesday into the sea off the Korean Peninsula.
"It is new for a United States government to act in a similar way, but I don't see people in Seoul going out and stocking up on rice", he said.