Four planeloads of soldiers from El Salvador landed in Haiti on Friday, days after the Central American nation’s president angrily threatened Haitian gangs that ambushed a group of Salvadoran soldiers over the past weekend who remain missing.

The four flights carrying 350 Salvadoran military landed a day after El Salvador sent 100 special forces troops to Haiti in response to the gang attack. One of the aircraft carrying the Salvadorans on Friday was a U.S. military plane. Two flights from the United States arrived in Port-au-Prince’s Toussaint Louverture International Airport on Friday as well, originating from Washington Dulles International Airport.

The flights were first reported by Haiti analyst Jake Johnston, an international researcher at the Center for Economic and Policy Research.

The Miami Herald has learned that one of the aircraft carrying the Salvadoran troops, a U.S. C-130 military transport, was provided by the Pentagon at the request of the U.S. State Department. It was unclear Friday evening if the other three chartered flights carrying Salvadoran military, including a Boeing 737 that turned up unannounced before 10 p.m., had been provided by the U.S. government.

The arrival of the flights and the participation of U.S. military aircraft raises questions about whether the reaction of the president of El Salvador — a strategic economic and security partner of the United States — to the ambush of his troops is drawing Washington deeper into the armed crisis in Haiti.