A new assessment by USA intelligence officials reportedly says North Korea has produced a miniaturized nuclear warhead that can fit inside intercontinental ballistic missiles, a development that led to a fiery rebuke from President Donald Trump.
Trump made the comments during a briefing from his golf course in New Jersey following a report that Pyongyang has developed the capability to launch a nuclear attack against mainland U.S. cities.
During an hour-long phone call, Moon and Trump said they would continue cooperating to rein in North Korea, particularly ahead of a regular joint military drill set for late August, South Korean presidential office spokesman Park Su-hyun told a media briefing.
Adding to fears the secretive state's missile programme is gathering pace, a leaked report from U.S. intelligence published in the Washington Post suggested the one-party state has successfully miniaturised nuclear warheads which can fit inside missiles.
The U.N. Security Council unanimously imposed new sanctions on North Korea on Saturday aimed at pressuring Pyongyang to end its nuclear programme.
Tension has been running high since the nuclear-armed North staged two successful ICBM tests last month, sparking global alarm over its rapidly-advancing weapons capabilities.
The same study says that while sanctions have yet to curb North Korea's nuclear program, increasing restrictions is the option that receives the most support from the American public - 76 percent.
In recent months, North Korea has conducted a series of missile tests that have incensed the White House.
Fox News cites US officials who said the reclusive nation is continuing its aggressive military moves despite USA and UN warnings not to.
Using his favourite messaging tool, Twitter, Trump, wrote, "After many years of failure, countries are coming together to finally address the dangers posed by North Korea".
Kazianis said it still is not clear whether North Korea has developed heat shield technology required to allow a missile to leave and re-enter the atmosphere.
"Today's news makes clear that much more than these sanctions is required to protect US interests, said Jay Lefkowitz, a former USA special envoy on human rights in North Korea".
Officials at the agency have not commented.
Officials in the USA believe North Korea has up to 60 nuclear weapons.
United States stocks fell after Mr Trump's comment, with the S&P 500 falling to a session low.
In a separate tweet on Tuesday, Trump praised his administration's work at containing the North Korea crisis, even as the outcast nation remained unbowed.