Kings, prime ministers and presidents, including President Bush, have convened at U.N. headquarters in New York for the three-day event, which was originally organized to discuss combating poverty but has changed its focus toward reforming an organization hobbled by corruption and mismanagement charges.
In his opening statements before the summit, Annan applauded some breakthroughs achieved in a reform document approved Tuesday by the organization's 191 member states, but said the plan failed to accomplish the significant changes needed, Reuters reported.
In March, Annan proposed a sweeping set of reforms to the organization that had led to a flurry of negotiations among member states, particularly within the last month.
Only some of his proposals, including creating a Peacebuilding Commission and an agreed responsibility to protect civilians against genocide, war crimes and ethnic cleansing, were left in the 35-page document. Others, such as expanding the Security Council and calling for nuclear nonproliferation, were dropped completely or left for later discussion.
"[L]et us be frank with each other, and the peoples of the United Nations. We have not yet achieved the sweeping and fundamental reform that I and many others believe is required," Annan told the assembled leaders, Reuters reported.
"Our biggest failing is on nuclear nonproliferation and disarmament," he said.
Annan and the U.S. delegation, led by new Ambassador John Bolton, have insisted the document is only the start of the reform effort at the United Nations.
"This is not the end of the reform effort," said U.S. Undersecretary of State R. Nicholas Burns, according to the Washington Post. "It really is the beginning of a permanent reform effort that must be underway at the United Nations."
World leaders are expected to officially endorse the reform document Friday.
President Bush, meanwhile, told the summit Wednesday that the United States is prepared to drop trade tariffs if other nations would do the same.
"Today I broaden the challenge by making this pledge: The United States is ready to eliminate all tariffs, subsidies and other barriers to the free flow of goods and services if other nations do the same," he told the summit, according to Reuters.
President Bush also touched on global terrorism, telling attendees that war alone would not win the fight against terrorism and states must tackle keeping weapons out of the hands of the oppressed.
"We must defeat the terrorists on the battlefield and we must also defeat them in the battle of ideas," he said.
He pushed for Security Council approval -- which followed afterward -- of a resolution calling upon nations to enact laws banning the incitement of terrorism and denying safe havens to those found guilty, according to the Associated Press.