NEW YORK CITY (USA TODAY) – President Trump began his first United Nations trip on Monday by calling on the international body to improve the way it does business, and to have it pay more of the costs for joint projects like peacekeeping.

"In recent years the United Nations has not reached its full potential because of bureaucracy and mismanagement," Trump told delegates from other countries, calling on the organization to invest "more in people and less in bureaucracy."

Trump, a long-time critic of the U.N., also made reference to his frequent campaign trail complaint that the United States bears an oversized share of the costs for U.N. activities. "We must ensure that no one and no member state shoulders a disproportionate share of the burden," Trump said, "and that's militarily or financially."

The U.S. covers about 22% of the U.N. budget.

Speaking for about four minutes at his first United Nations event, Trump said he wants to change "business as usual," and see the organization develop unspecified "metrics" by which it can measure its management and efforts to promote peace and security.

The president also promoted one of his own business projects, an apartment tower across from the United Nations building, and credited its success in part to the existence of the U.N.

Trump's comments at the special forum – entitled "Reforming the United Nations: Management, Security, and Development" – kicked off four days of meetings and receptions at the U.N., topped by a Tuesday morning speech to the entire 193-member General Assembly.

Nikki Haley, Trump's ambassador to the United Nations, described the reform meeting as a sign that "it truly is a new day at the United Nations."

Having run for president in part on an "America First" platform, Trump had harsh words in particular for the United Nations.

During the 2016 campaign, Trump at one point said "the United Nations is not a friend of democracy; it's not a friend to freedom." He has also described the U.N. as "a club for people to get together, talk and have a good time."

Some U.N. members, meanwhile, have expressed concern that Trump's preference for unilateral action could undermine the global trading system and under cut U.N. efforts promote peaceful resolutions of international disputes.

Trump re-took the world stage more than two months after attending a trip of international summits – NATO, the G-7, and the G-20 – that featured disputes over trade, climate change, and the U.S. commitment to mutual defense of NATO allies.

In preparing for his week-long series of U.N. meetings, Trump's major objective is to rally global support for pressuring North Korea into giving up nuclear weapons, or at least stop threatening to use them against the United States and its allies in Asia.

While Trump and his aides said they want to resolve the dispute diplomatically, they have also reserved the military option. Over the weekend, Trump added to the tension by describing North Korean leader Kim Jong Un as "Rocket Man."

Many White House officials are out and about in New York this week.

Gary Cohn, director of the National Economic Council, attended an "energy breakfast" with U.N. counterparts.

During the meeting, the White House said, Cohn repeated statements by other aides that the United States will maintain plans to withdraw from the Paris climate change agreement unless it can negotiate more favorable terms.

"This position was made very clear during the breakfast," the White House said in a statement.

Trump, who paused during the morning to tweet out a tribute to the U.S. Air Force on its 70th anniversary, also plans to address his concerns about Iran on Monday.

The president is considering whether to de-certify the nuclear agreement that predecessor Barack Obama reached in 2015. While Iran agreed to give up the means to make nuclear weapons as the U.S. and allies reduce economic sanctions, Trump says Iran isn't living up to "the spirit" of the deal.

Trump's meetings include Israeli Prime Minister Benjamin Netanyahu, who has urged the United States to "fix" the nuclear agreement or scrap it.

Iran's Supreme Leader Ayatollah Ali Khamenei said over the weekend that his country would respond to any "wrong move" by the United States.

Trump planned to cap his first day at the United Nations at a working dinner with Latin American leaders. Their topics include the economic and democratic instability in Venezuela, and the impact it has on the region.