UNITED NATIONS (REUTERS) - President Donald Trump's first encounter with the United Nations on Monday (Sept 18) started on a conciliatory note.

US President Donald Trump said: "The United Nations was founded on truly noble goals."

And he called on the world body to embrace reforms so that it might better achieve those goals.

Said Trump: "In recent years the United Nations has not reached its full potential because of bureaucracy and mismanagement."

While that might seem like unwelcome criticism, it's a view apparently shared by UN Secretary General Antonio Gutteres.

Says Gutteres: "Someone recently asked, what keeps me up at night? And my answer was simple: bureaucracy."

Monday's comments made at an event titled Reforming the United Nations, which UN Ambassador Nikki Haley described as "truly a new day" for the UN.

Trump's praise of the UN mission was a marked departure from his broadsides during the presidential campaign.

Said Trump on March 30, 2016, then a US presidential candidate: "What do we get out of the United Nations? Do you ever hear that the United Nations solved a problem?"

But now Trump has a problem he seems to need the UN to help him address: North Korea's missile program.

The change in tone on Monday coming after reports the US is now considering remaining in the Paris climate accord - if certain terms are met - after Trump pledged to withdraw.

And as the US appears unwilling to cancel the six-nation Iran nuclear deal despite the White House repeatedly claiming Tehran was in violation of the spirit of the deal.

But Tuesday will be the true test, as Trump addresses the full General Assembly.

The world will be watching to see if the fiery nationalist has been tempered by cold reality.