"In recent years the United Nations has not reached its full potential because of bureaucracy and mismanagement", Trump said at the meeting, which was held on the sidelines of the UN General Assembly.
Reading carefully from a script, Trump promised the United States military would soon be the strongest it has ever been.
According to Trump administration officials, the U.S. president is expected to lay out how his own nationalist policies can work with the worldwide cooperation the United Nations represents and call on the body's other 192 members to confront threats such as North Korea more head-on.
The President questioned the 2015 nuclear deal with Iran.
"Rocket Man is on a suicide mission for him and his regime", Trump said of Kim.
"I will always put America first, just like you, the leaders of your countries, should put your countries first", he said, noting that "the nation-state remains the best vehicle for elevating the human condition". "But in fulfilling our obligations to other nations we also realize it's in everyone's interest to seek a future where all nations can be sovereign, prosperous and secure".
At the event on September 18, Trump "will express support for Secretary-General Guterres's reform efforts", White House spokeswoman Sarah Sanders said at a briefing on September 15. "We are prepared to take further action if the government of Venezuela persists on its path to impose authoritarian rule on the Venezuelan people".
"We can not stand by and watch", he said.
His fellow leaders here at the annual gathering here of more than 150 delegations are listening for signs of how closely Trump will align himself with the U.N.in the face of a series of global challenges, including North Korea, Syria and Iran. This is a time for statesmanship. The initiatives mostly focused on reforming the UN Security Council by increasing number of its permanent members or canceling the veto right.
But Trump has also voiced concerns that the U.N. and North Atlantic Treaty Organisation have relied too heavily on the United States and that other members should shoulder more of the economic and leadership burdens.
"I hope that this is a reasoned, already written speech and that he sticks to the written words and that he tries to give world leaders a sense that the U.S.is not about to abandon them", Najam said.