The Summit of the Americas has opened in Los Angeles, California. But the leaders of Mexico and some other countries are boycotting the event to protest the omission of Cuba, Venezuela and Nicaragua.
US President Joe Biden told leaders at the summit meeting on Wednesday, "Our region is large and diverse. We don't always agree on everything."
He added, "But because we're democracies, we work through our disagreements with mutual respect and dialogue."
Participants are expected to discuss issues such as migration and climate change through Friday.
The United States, which is hosting the meeting, did not invite the leaders of Cuba, Venezuela and Nicaragua. The White House press secretary said, "The president's principal position is that we do not believe that dictators should be invited."
Opposing this decision, Mexican President Andres Manuel Lopez Obrador skipped the summit and the leaders of Bolivia and Honduras also chose not to attend.
Multiple US media say the United States is losing its influence in the region.
Biden wants results on the migration issue, which is of high concern to many Americans, ahead of the midterm elections later this year. It's unclear whether he can introduce effective measures with the absence of the president of Mexico, which borders the US.