NEW YORK — President Trump called on the United Nations to enact reforms to the world body, pledging Monday in his debut here at the annual General Assembly meetings that he and his administration will be “partners in your work.”

Speaking at the opening session of the four-day conference, Trump said the organization founded in 1945 has “not reached its full potential” in recent years because of a bloated bureaucracy and “mismanagement.”

“We encourage all member states to look at ways to take bold stands at the United Nations with an eye toward changing business as usual and not being beholden to ways of the past which were not working,” Trump said, flanked by U.N. Ambassador Nikki Haley and Secretary General António Guterres.

Trump had spoken dismissively of multilateral institutions, including the United Nations and NATO, during his campaign, promoting an “America first” agenda aimed at reducing the United States' interventionism abroad in favor of domestic priorities.

His fellow leaders here at the annual gathering of more than 150 delegations are listening for signs of how closely Trump will align himself with the United Nations in the face of a series of international challenges, including North Korea, Syria and Iran.

Speaking briefly with reporters, Trump riffed off of his campaign slogan, "Make America Great Again." Trump said his main message is: "Make the United Nations great. Not again. Make the United Nations great. Such tremendous potential, and I think we'll be able to do this."

Introducing Trump, Haley said the former business mogul is “no stranger to change” and added that he “sees great potential, not just in the reform among members, but in the United Nations itself.”

Ahead of the meetings, Haley had lauded the United Nations for a pair of recent votes to enact severe economic sanctions on North Korea over its nuclear and ballistic missile programs. The sanctions seek to curtail oil imports to Kim Jong Un's regime and block exports from the country.

The White House said Trump spoke by phone with Chinese President Xi Jinping, who is not attending the General Assembly, to discuss North Korea's efforts to "destabilize" Northeast Asia.

"The two leaders committed to maximizing pressure on North Korea through vigorous enforcement of United Nations Security Council resolutions," according to the White House statement.

But Trump has also voiced concerns that the United Nations and NATO have relied too heavily on the United States and that other members should shoulder more of the economic and leadership burdens.

“We must ensure that no one and no member state shoulders a disproportionate share of the burden, and that's militarily or financially,” Trump said. “We also ask that every peacekeeping mission have clearly defined goals and metrics for evaluating success.”

Trump couldn't resist putting in a plug for one of his development projects — Trump World Tower, a residential skyscraper across the street from the U.N. headquarters that was completed in 2001. Former New York Yankees star Derek Jeter and White House adviser Kellyanne Conway have been tenants, and the government of Saudi Arabia purchased the 45th floor.

“I actually saw great potential right across the street, to be honest with you,” Trump said, “and it was only for the reason that the United Nations was here that that turned out to be such a successful project.”

After the opening session, Trump traveled to the Lotte New York Palace Hotel for separate meetings with Israeli Prime Minister Benjamin Netanyahu and French President Emmanuel Macron. Sitting next to Netanyahu, Trump told reporters his administration was working "very hard" on a peace deal between Israel and the Palestinians.

Peace "would be a fantastic achievement," Trump said. "We are giving it an absolute go. I think there's a good chance it could happen."

Trump and Netanyahu were also expected to discuss the Iran nuclear deal, which Netanyahu strongly opposed. The Trump administration faces a deadline in mid-October to determine whether Tehran has lived up to the terms of the agreement. Although administration officials have acknowledged that Iran has abided by the technical terms, they have emphasized that the country has violated the "spirit" of the deal by supporting terrorism in the Middle East.

"We'll see very soon," Trump said, when asked by a reporter whether he will pull the United States out of the Iran deal.

Trump is scheduled to join Latin American leaders for a working dinner to discuss issues including the political crisis in Venezuela.