TECÚN UMAN, GUATEMALA — Clutching a folder holding his ID documents, Steven Martinez stood uncertainly in no man’s land — the middle of the Rodolfo Robles bridge connecting Guatemala to Mexico — in this frontier outpost named for a Mayan warrior.

Martinez, a Honduran migrant, was determined to cross legally into Mexico en route to the US. But with increased border security as Mexico begins to deploy thousands of elite troops on its southern border with Guatemala, it was unlikely that Martinez would be able to cross.

Last month, more than 144,000 migrants crossed into the US, a 32 percent increase since April and the highest monthly tally in seven years, according to US Customs and Border Protection data.

“We’re going to try to cross legally,” said Martinez, who was accompanied by his heavily pregnant wife, sister and two young nieces, as they made their way to the Mexican side of the bridge.

The 27-year-old mechanic said the family was fleeing violence from MS-13 gang members who had pressured him to join in his impoverished hometown in the mountains of central Honduras.

His sister, Sulma Aquino Garcia, 23, told The Post she had been in hiding for the last two years with her daughters — aged 5 and 2 — because her abusive husband had tried to kill them. Aquino said she had recently spent time in hospital recovering from beatings and a gunshot wound.

“If we don’t make it across the bridge, we’ll take the other way,” said Martinez.

The “other way” is the nearby Suchiate River, where rafts made from planks of plywood strapped to inner tubes ferry passengers and goods between the two countries hundreds of times a day.

Unlike the border bridge, nobody on either bank currently patrols the 10-minute voyages across the 150 yards of muddy water. All that could change Monday, when Mexico begins its troop deployment along its border with Guatemala.

“Most of the migrants cross with us,” said Jose Lopez, 62, manager of a rafting operation on the Guatemalan side of the river. Lopez, who has two silver front teeth and is known by his nickname “El Chapero” or “the hustler,” has been working the river for 35 years.

Lopez said he has an agreement with the “balseros,” or rafters, on the Mexican side to work alternate days. He charges 10 quetzals — the equivalent of about $1.50 —per passenger.

Last October, a caravan of thousands of Central American migrants descended on this jungle city where currency changers wave wads of pesos and quetzals at passers-by from open-air stalls. When Mexican authorities prevented them from crossing the bridge, the migrants rioted and broke through a border fence. Mexican authorities responded with a phalanx of riot police and pepper spray.

Since then, business has been booming for Lopez, who said thousands lined up to take the rafts, which are a few minutes’ walk from the bridge. Police didn’t often patrol the rafts, which are used by local merchants and shoppers to push pallets of Coca-Cola and other goods back and forth every day.

Following Friday’s agreement with the US in which Mexico caved to pressure from President Trump, Lopez expects even more migrants taking to the river, even though they will now be at greater risk of being apprehended once they reach the Mexican side.

“The river traffic goes up and down,” said Lopez, keeping a record of the day’s earnings on a stray piece of cardboard. “Soon it will be way up again.”

In addition to Mexican troops making the crossing for migrants far more difficult, the US Department of Homeland Security also promised to send dozens of Border Patrol agents and other advisers to help Guatemalan authorities set up checkpoints and tighten border security to crack down on migrants traveling through that country.

Candidates in the country’s upcoming presidential elections have seized on the news in their campaigns, stoking fear that the US will send soldiers. A front-page headline in Monday’s Prensa Libre, a Guatemalan daily, read, “We reject American troops” at the border.

“We are selling our sovereignty for the umpteenth time,” said Isaac Farchi, a candidate in Guatemala’s June 16 presidential race, referring to the DHS advisers scheduled to arrive in Guatemala. “I don’t know why Guatemalans think we need foreigners here.”

In the past, Central American migrants crossing through Mexico told stories of being forced to pay bribes to Mexican border officials to make their way to the US. It’s unclear whether the Mexican military presence at the country’s southern border will deter the flow of migrants.

And no one in this border city knows how that will affect the river migrants, although some said they would try to cross at more isolated parts along its 100-mile length.

Last Saturday, a group of Haitians carved out space on the ground outside a ramshackle hotel near the international bridge.

“We just got here a few hours ago, and we have no money or documents,” Larose Yonald, 29, told The Post, adding that he and nine family members had been on the road for two months, mostly walking from Chile, where they had lived for the last two years.

“They don’t like black people in Chile,” he said, adding that the family was headed to the US, where they have relatives in New York and Miami.

“As soon as we get the money, we are crossing by the river,” Yonald said.