Salvador’s troop presence in Haiti has swelled to at least 600, according to a top researcher, a reflection of President Nayib Bukele’s efforts to find four kidnapped soldiers in the troubled Caribbean nation.

At least three charter flights from El Salvador arrived on Tuesday, and a fourth was en route. Jake Johnston, the Haiti expert, said there’s been a steady stream of flights carrying El Salvadoran soldiers and equipment to the country. Reuters reported that the number is about 1,000, citing a security official in Haiti. The government of El Salvador didn’t immediately respond to requests for comment, and the United Nations-backed Gang Suppression Force, or GSF, said it couldn’t provide details.

The crisis intensified on Oct. 18, when the Salvadorans were reported missing. They were part of the GSF, a multinational group that’s seeking to restore peace in Haiti under the authorization of the UN Security Council. Gangs have ravaged much of the country and have seized large swaths of the capital while Haiti tries to organize long-overdue elections.

Days after the disappearances, Bukele sent a first group of troops to Haiti, where he said they would crush “satanic” criminal groups like they had in his home country, where he has incarcerated an estimated 90,000 people on gang-related charges.

“Bukele is someone who has a lot wrapped up in his image as this ultimate crime fighter,” said Johnston, the director of international research at the Center for Economic and Policy Research and the author of a book about Haiti. “And I do think that it’s something that Bukele and others are interested in selling to the world and exporting to the world. Theoretically, this could be an for the Bukele model.”Flight tracking websites show the arrival of three Boeing 747-400s on Tuesday from San Salvador, with a fourth scheduled to land later in the day.

The surge represents a significant uptick in international military forces in Haiti. The GSF is authorized to have 5,500 members on the ground, but has less than half that number. El Salvador, Kenya, Chad, Sri Lanka and Jamaica are among the nations that have sent troops for the effort.

On Saturday, Bukele denied reports that the bodies of the missing Salvadoran soldiers had been recovered. A day later, the GSF said it had received remains it “suspected of being those of the four personnel from El Salvador” but couldn’t confirm their identities. Since then, neither the GSF nor Bukele have commented on the corpses.

The Dominican Republic, which shares a 392-kilometer (244-mile) border with Haiti, is providing diplomatic and logistical aid, including providing medical care to wounded GSF troops, shuttling soldiers into the country and providing economic support, said Dominican Foreign Minister Victor Bisonó.

But longstanding animosity between the neighboring countries means that putting Dominican boots on the ground is inadvisable — akin to Russians participating in an international effort in Ukraine, or Chile in Bolivia, he said.

“Dominican forces in Haiti would open up issues that would not be desirable,” he said in a phone interview, alluding to the nation’s long and tangled history.

Haiti is trying to hold its first elections in more than a decade. While 18 presidential candidates have registered ahead of an Oct. 31 deadline, no firm date has been set for the actual election.

“We have to make clear that the solution to Haiti’s problems has to come from Haiti,” Bisonó said. “No other country can do that for them, and much less the Dominican Republic.”