President Joe Biden’s efforts to rally international support during this week’s Summit of the Americas took a blow when Mexican President Andrés Manuel López Obrador confirmed he will skip the summit. On Monday, President Obrador said he would be sending Mexican Foreign Minister Marcelo Ebrard instead.

“I sent word to President Biden that I will visit him in July,” López Obrador said. “I am going to meet with him at the White House and I want to discuss with him the issue of the integration of all America.”

The Mexican president’s decision to skip was in response to the United States’ decision to bar Cuba, Nicaragua and Venezuela from the Summit of the Americas. State Department Spokesperson Ned Price defended the decision Monday, saying “the challenges that these three regimes pose to some of the central tenets of the summit… were just insurmountable.”

“[Cuban residents] have been deprived of rights that should be universal. The same, of course, could be said of what has happened in Nicaragua, where we’ve seen an increasing, increasingly constricted space for civil society,” Price said. “And of course, Venezuela, under the Maduro regime, a regime that we don’t recognize.”

López Obrador had been leading a chorus of mostly leftist leaders pushing the U.S. to invite the three countries to the summit. Other leaders, including from Guatemala, Honduras and El Salvador — three big drivers of migration to the U.S. — have indicated they’ll stay away too.

While the Mexican president won’t be at the Summit for the Americas, a migrant caravan of more than 6,000 people might be. The caravan, made up of mostly people from Venezuela, left the border city of Tapachula Monday.

Migration activists said the group could be one of the region’s largest migrant caravans in recent years. The timing of their journey was meant to draw attention to their plight as the summit was proceeding.

“What do I ask of the United States? That they help us, that they give us support,” Venezuelan migrant Inalia Mendoza said Monday. “If they can go to Venezuela and solve that situation. Look, we would be happy to return to our homeland, that’s what I long for the most: to return to my homeland.”

The Associated Press and Reuters contributed to this report.