WASHINGTON — The Biden administration expelled nearly 4,000 Haitians on 36 deportation flights in May — a significant increase over the previous three months — after renegotiating agreements with the island nation, which has been crippled by gang violence and an expanding humanitarian crisis.

Over the past year, a growing number of Haitians have been making the journey through the jungles of South America to dangerous stretches of northern Mexico, then crossing into the United States. Recently, many have also been trying to reach Florida by boat. They have been part of a record wave of migration at the border with Mexico.

While the number of Haitians crossing into the United States has increased recently, it is far from the biggest migration challenge facing the country. It just happens to be one of the easiest for the administration to manage.

An emergency public health rule has allowed border officials to quickly expel migrants during the coronavirus pandemic, but the Biden administration is limited in terms of where it can send flights. For the most part, Mexico will accept migrants turned back from the United States only if they are from El Salvador, Guatemala, Honduras, Mexico and, in limited cases, Cuba and Nicaragua.

Others must be flown back to their countries, but U.S. border officials have to allow most Cubans, Nicaraguans and Venezuelans — who make up a significant portion of those recently crossing the border — to stay and eventually face removal proceedings. A lack of diplomatic relations with those countries prevents the United States from sending flights there.

But the U.S. government also cannot send as many removal flights as it would like to countries with which it has strong diplomatic ties.

“All deportation policy relates to foreign policy,” said Yael Schacher, the deputy director for the Americas and Europe for Refugees International, an advocacy group.

But some say that the instability in Haiti, especially since the assassination in July of its former president, Jovenel Moïse, has made it relatively easy for the U.S. government to send flights there. At one point last month, Haitians represented about 6 percent of the migrants crossing the border with Mexico but occupied 60 percent of expulsion flights, according to flight records and internal border data.

“We do not have a government in Haiti that can make those decisions,” Guerline M. Jozef, the president of the Haitian Bridge Alliance, an advocacy organization, said of the number of expulsion flights the country could accept. Many Haitians do not recognize the current government in Port-au-Prince as legitimate.

The situation in Haiti has worsened over the past year. The International Organization for Migration, the largest nongovernmental aid group there, said that there were more than 200 kidnappings in May. Poverty is everywhere, and nearly half the country does not have adequate access to affordable and healthy food, according to the United Nations.

In September, the Biden administration gave the organization $13.1 million intended to help Haitians getting off expulsion flights, providing cash and other assistance to help them to reintegrate. Many had been living in other countries in South America for years before making the journey to the United States.

The systemic issues that drive migration out of Haiti are expected to come up during the Summit of the Americas in Los Angeles this week. Haiti’s interim prime minister, Ariel Henry, is in attendance.

President Biden ran for office promising to bring compassion to U.S. immigration policies, particularly those involving asylum. But rolling out new policies amid a sharp increase in migration and during a pandemic has proved difficult. Some Trump-era policies remain in place.

In September, about 15,000 migrants, many of them Haitian, crossed the border into Del Rio, Texas, over the course of a few days. That month, the United States sent a record 58 expulsion flights to Haiti, according to data collected by the International Organization for Migration, which tracks the flights.

The number of flights per month decreased after that but rose again in January, when there were 36. There were a total of 39 flights from February to April, and the number shot up again in May, with many families and children younger than 3 aboard the 36 flights that month.

After an infant died in a Haitian hospital shortly after arriving on an expulsion flight in January, the International Organization for Migration asked the Biden administration to halt the expulsions of young children. .

From May 19 to 26, U.S. border officials encountered 1,868 Haitians who had crossed the southwestern border, according to internal government data. During that period, there were 21 expulsion flights to Haiti. In comparison, over the same period, they countered 5,264 Guatemalans and 4,453 Hondurans, and the United States sent seven expulsion flights to each country.

“Haiti can do nothing to slow deportations,” said Daniel Foote, a former special envoy to Haiti who resigned last year in protest of the Biden administration’s handling of the mass migration crisis in Del Rio. Yet sending thousands back to Haiti, which he described as a failed state, would only exacerbate the situation, he said.

“It’s counterproductive to a stable Haiti, which is critical to stop them from migrating in the first place,” Mr. Foote said, referring to Haitian migrants.

Officials at the Department of Homeland Security said there had not been any policy change regarding Haitian expulsions. The White House declined to comment.

One federal official, speaking on the condition of anonymity to discuss a foreign policy matter, said the expulsion flights to Haiti were not disproportionate to those sent to other countries. The official said the government negotiated agreements with other countries about the number of flights it could send. The negotiations allowed for flexibility so that the United States could quickly increase the number of flights to a certain country if there were a need. That was what had happened with Haiti, he said.

Since September, more than 25,000 Haitians have been expelled from the United States and returned to Haiti. There does not appear to be an end in sight. Recently, anticipating a change in border policy that has been put on hold, more Haitians have waited in northern Mexico with plans to cross the border and ask for asylum — a legal right that has been blocked since the beginning of the pandemic.

“I don’t have another plan except to go to the U.S. — go there and work,” Carlos Montius, 35, said last month. Mr. Montius, a Haitian from Port-au-Prince, said he had been staying in Reynosa, Mexico, for the better part of a year.

The Biden administration has taken steps to address the instability in Haiti, though some say it is far from enough.

At two different points last year, the administration extended temporary humanitarian protections for Haitians who were already living in the United States. The administration also briefly stopped expulsion flights to Haiti after it was hit by a devastating earthquake in August.

The Biden administration also reinstated the Haitian Family Reunification Parole Program, which the Trump administration ended in 2019. The program gives eligible U.S. citizens and lawful permanent residents the ability to apply for parole for family members in Haiti. But there have been delays in getting the program up and running because administration officials believe it is unsafe to send U.S. government employees to Haiti to process the applications, according to a Senate aide who spoke on the condition of anonymity to discuss an internal matter.

This year, the administration has authorized 55,000 temporary work visas, with 18,000 set aside for people from El Salvador, Guatemala, Honduras and Haiti. The Department of Homeland Security does not track how many of those went to people from each country.

The recent uptick in expulsions of Haitians has again drawn criticism that the Biden administration treats Black migrants differently than others, an allegation it has repeatedly denied.

“The administration must commit to racial equity in its immigration policy and address the anti-Black racism that disproportionately impacts Haitian migrants at the border,” said Senator Bob Menendez, Democrat of New Jersey and the chairman of the Foreign Relations Committee. He and others pointed to the swift action that the United States took to allow Ukrainians into the country as they fled the Russian invasion.

“We have not seen a single new policy to address the high number of displaced Haitians in the Western Hemisphere,” Mr. Menendez added, “other than to expel them as quickly as possible.”

It is a delicate issue for the White House after the public outrage last year — including from the president — after the Border Patrol’s response to the Black migrants crossing into Del Rio. At the time, Border Patrol agents on horseback were photographed corralling migrants, images that some people said were suggestive of slavery.

One image found its way onto an unofficial Border Patrol commemorative coin. The origin of the so-called “challenge coin” is under investigation by the Customs and Border Protection’s Office of Professional Responsibility.

The office has been investigating the conduct of the agents who corralled migrants in Del Rio last year. The administration promised a swift internal investigation into the episode, but there has yet to be a public announcement regarding any findings.

Mr. Menendez called the lack of public findings “unacceptable.” Of the coin, he said, “Anyone who would create or circulate these racist tokens are unfit to enforce our immigration laws and have no place anywhere in our federal government.”

Kirsten Luce contributed reporting from Reynosa, Mexico.