Developing world leaders, including virulent US foes, met at the summit in Havana without Cuba's communist strongman Fidel Castro, whose convalescence kept him away from the spotlight.
Among the prominent leaders speaking at the two-day summit was Iran's President Mahmoud Ahmadinejad, who insisted Tehran's controversial atomic program had strictly peaceful objectives, and claimed the United States was the real nuclear threat.
"Why should people live under the nuclear threat of the United States?" he asked at the summit of the 118-member NAM.
"What is the UN Security Council waiting for to react to those threats?"
He urged his counterparts to help "counter attempts to prevent Iran from developing its peaceful nuclear activity."
Raul Castro, and Venezuela's President Hugo Chavez, also delivered blistering condemnations of the United States, while Indian Prime Minister Manmohan Singh called for "moderation, harmony and reason."
Mr Singh also urged NAM leaders to make a priority of countering terrorism.
"If NAM is to be relevant in today's circumstances, it cannot afford to equivocate on the subject of terrorism," he said.
Singh planned to hold talks on the sideline of the summit with Pakistani President Pervez Musharaf, who said the two countries had a "historic opportunity" to restart negotiations on the Kashmir dispute.
Talks over the disputed Himalayan Kashmir region, divided between the two countries but claimed in its entirety by both, have been stalled since July, when 183 people were killed in bomb attacks in Mumbai.
Kofi Annan, an invited guest at the summit, urged NAM leaders to respect human rights and prevent crimes against humanity.
The movement includes several states that face harsh criticism for their human rights records, including North Korea, Zimbabwe and Belarus.
"We need governments of the South to fulfil their obligations to their people at home ... Ending suppression of opposition groups and the media.
Taking serious and sincere measures against corruption," Annan told the leaders.
He said governments also had a duty to "protect populations from genocide, war crimes, ethnic cleansing and crimes against humanity."
The summit is due to conclude with the adoption of a draft document calling for a reform of the UN Security Council and stressing the need for increased cooperation among developing countries in order to counter overwhelming US influence.