Japan says it is deploying the Patriot Advanced Capability-3 (PAC-3) system in Shimane, Hiroshima and Kochi in western Japan, after North Korea threatened to fire ballistic missiles over the country towards the US Pacific territory of Guam.
Trump warned last week that North Korea would be met with "fire and fury" if it continued to threaten his country.
North Korea's Minju Joson newspaper, meanwhile, lashed back at the U.S.in an editorial Saturday.
"The US military is locked and loaded every day", Mr McMaster said, repeating Mr Trump's threat.
On Tuesday, the North Korean leader was quoted by the KCNA state media outlet saying he will wait and see "if the Yankees persist in their extremely unsafe, reckless actions" before going forward with the missile test targeting the Guam area. It also said that the two "reiterated their mutual commitment to denuclearization of the Korean Peninsula".
But he rejected talk of the US being on the "cusp of nuclear war". The two envoys reportedly first engaged in negotiating the release of USA college student Otto Warmbier two months ago. However, now it is standing before a deteriorating reality and security instability due to North Korea.
The White House said in a statement that Trump and Xi "agreed North Korea must stop its provocative and escalatory behavior".
Advocates for diplomacy see hopeful signs in the Trump administration's willingness to talk without rigid preconditions. "So it could be a hint, sort of a model to get us out of this game of chicken", Delury said.
USA intelligence does not indicate an imminent nuclear war with North Korea, the chief of the Central Intelligence Agency said Sunday, after a week of bellicose rhetoric between the two sides.
He said previous presidents had also used strong words to warn off Pyongyang, pointing out Barack Obama said past year that "we could, obviously, destroy North Korea with our arsenals".
Moon also reassured Pyongyang that Seoul does not seek the collapse of the Kim regime or the unification of the Korean Peninsula through force or "absorption", and renewed calls for dialogue and cooperation.
The message ended with a threatening statement claiming that the North Korean military has "the ability to fight any kind of war that the U.S. wishes for and is prepared to launch fire towards USA territory, awaiting a final order to carry out the attack". Beijing is North Korea's biggest economic partner and source of aid.
With global sanctions preventing Moon from restarting economic aid and joint ventures, the South Korean leader has few incentives to entice the North.
Some analysts said Mr Kim was seeking a similar quid-pro-quo this time around, using the Guam missile threat as leverage.