Difficulties in obtaining supplies, including medical equipment, and in transferring money to fund aid programmes could have a direct impact on health and nutrition levels throughout North Korea, aid groups say.
"Well, we're going to see what happens with North Korea".
The US is even more determined to continue its peaceful pressure campaign, Tillerson said, with the goal of "setting the conditions for North Korea to engage in serious negotiations toward the complete, verifiable, and irreversible abandonment of its nuclear weapons programs".
That remark caused the White House to reiterate President Trump's views on the situation "have not changed".
Tillerson also dismissed concerns that United Nations sanctions are having an impact on North Korea's humanitarian crisis, saying Pyongyang "hypocritically spends billions" on military programs "while its own people suffer great poverty".
As long-term allies of North Korea, the two countries are key players in enforcing the sanctions.
Mattis did detail what led officials to conclude the missile does not yet pose an immediate threat to the US, according to Reuters.
American president Donald Trump has publicly undermined his secretary of state, Rex Tillerson, for the nth time.
Anxieties about U.S. power could combine with a crippled economy and the loss of China and Russian Federation as allies to force the belligerent autocracy to cool down its nuclear programme.
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On Tuesday, Tillerson said at the Atlantic Council think tank in Washington that "we are ready to have the first meeting without preconditions".
"We are looking at North Korea which within the next 12 to 18 months will make a nuclear missile to an intercontinental range ballistic missile that could reach London and we can't deal with that", he said. "We do not regard this claim as an empty threat".
Since the spring, the USA has run what it calls a "peaceful pressure campaign" against North Korea.
Tillerson extended that challenge to other countries that have been slow to fully implement existing resolutions on North Korea, saying that it calls "into question whether your vote is a commitment to words only, but not actions".
He said "our hope remains that diplomacy will produce a resolution". He urged an immediate re-establishment and strengthening of government and military communications.
In his briefing to Friday's meeting, U.N. Secretary-General Antonio Guterres offered his "good offices" to avoid the dispute over the "alarming and accelerated pace" of North Korea's nuclear and missile program accidentally escalation into conflict.
Sen. Lindsey Graham, R-S.C., who's discussed North Korea while golfing with Trump, told the Atlantic magazine this week that he believes "there's a 3-in-10 chance we use the military option" and a 70 percent chance that North Korea again tests a nuclear bomb.
Information for this article was contributed by Matthew Pennington, Edith M. Lederer, Mari Yamaguchi, Jerry Harmer and Ken Moritsugu of The Associated Press; and by Nick Wadhams, Kambiz Foroohar and Justin Sink of Bloomberg News.