Mexico City, Mexico - When Donald Trump kicked off his campaign for the US presidency with the notorious line about Mexican migrants "bringing drugs, bringing crime, they're rapists" it scandalised everyone south of the Rio Grande.

When he signed off on his border wall, still insisting Mexico pay for it, the indignation went off the scale.

Tens of thousands marched through Mexico City in opposition this Sunday while the government has earmarked $50m for consular protection for its citizens stateside.

President Enrique Pena Nieto has personally welcomed back some of the first to be deported under the Trump administration in a show of unity - and condemnation of the now even tougher stance against undocumented migrants of the US.

But the Mexican government's concern about how its citizens are treated in the US sits incongruously with its own attitude towards the migrants passing through Mexico which rights organisations have described as hypocritical.

In July 2014, the government unveiled a new plan called "Programa Frontera Sur" after the US exerted pressure on the country to stop a surge in the number of child migrants heading from Central America to the states.

'Invisible wall'

"Frontera Sur" was ostensibly designed to protect migrants, but it actually resulted in a noticeable increase in the number of checkpoints and border patrols in the south of the country. What analysts and activists have dubbed Mexico's own "invisible wall" succeeded in doubling the number of deportations from the country in the first full year of its implementation.

There's always been double talk - it seems that the Central American migrants don't matter, nothing is done to prevent the same human rights violations that Mexican migrants suffer in the US. Diego Lorente, lawyer

Those caught by authorities often end up in what is the biggest migrant detention centre in Latin America, built in the tropical border town, Tapachula. Here many people from Central American nations below Mexico like Honduras, El Salvador and Guatemala wait in the sweltering heat for their turn to be bussed back home.

Frequently, they are being sent back to grinding poverty, or the vicious gang violence that they fled in the first place.

In recent years, Honduras and El Salvador have both vied for the title of the world's most murderous country outside of a war zone.

NGOs have set up shop in the town to help some stay in Mexico.

Diego Lorente, a bearded lawyer who has been fighting for the rights of migrants for several years, told Al Jazeera there's a double standard in the Mexican authorities attitude towards migration.

"There's always been double talk - it seems that the Central American migrants don't matter, nothing is done to prevent the same human rights violations that Mexican migrants suffer in the US," Lorente said.

State authorities admit some Mexican officials are involved in the extortion, robbery, rape and even kidnapping of migrants. Alejandro Vila Chavez, the prosecutor for crimes against migrants in the southern state of Chiapas told Al Jazeera that last October his team burst open a ring of 21 local policemen who had kidnapped a group of migrants in the town of Chiapa de Corzo.

"They don't have the training to make them aware of their important duties," he said, speaking particularly about municipal police.

"Unfortunately, they lose sight of their role, using their authority and power in order to take advantage of migrants' vulnerability." Vila insisted that crimes against migrants in Chiapas were going down.

READ MORE: Central American mothers search for their missing sons

'Border security'

Nationally, the picture is different. A 2016 report from the human rights arm of the Organization of American States notes that "multiple cases involved the active participation of personnel from the National Migration office, municipal, state and federal police.

"A network of shelters for migrants, REDODEM, said that in 2015 officials committed 41 percent of the crimes against migrants they interviewed, 867 in total.

Federal authorities didn't respond to Al Jazeera's interview requests.

The complicity between some officials and Mexico's powerful gangs makes things more complicated still, particularly in the gulf states of Veracruz and Tamaulipas.

A "pollero", one of the guides that migrants pay to get them to the US border told Al Jazeera that in those states the Gulf Cartel and the Zetas demand a "tax" on everyone who passes through - a claim that migrants rights organisations have backed up.

READ MORE: Surviving Mexico's migrant trail

Even for those who pay, there is no guarantee of safety.

Migrants testify to having been raped, kidnapped and forced to work for organised crime. Deaths have also racked up. In one of the first, and worst, cases, 72 migrants were found shot dead in a ranch in Tamaulipas in August 2010. A survivor said they were executed by the Zetas after refusing to work for them.

Tens of thousands have simply disappeared. But, Mexican authorities often stonewall relatives trying to find out what has happened to them, according to Martha Sanchez Soler, head of the NGO "Movimiento Migrante Mesoamerica".

Sanchez Soler organises an annual caravan of Central Americans trying to find their loved ones.

"It's not convenient for the transit country [Mexico] to make known the crimes that are committed here, especially because there's lots of authorities that are colluding in them," she said, speaking to Al Jazeera during the last caravan in December 2016.

Rights groups have repeatedly said that the Programa Frontera Sur has directly increased the danger to migrants, by forcing them to cross isolated areas to evade checkpoints and patrols.

Despite the criticisms, the clampdown could actually represent one of Mexico's best bargaining chips in upcoming negotiations with the United States.

That's because by catching undocumented migrants further south, Mexico provides a valuable filter, stopping them from reaching the US. Recognising that, the US has itself contributed millions of dollars towards Mexico's southern border protection.

READ MORE: Cubans stranded in Central America try to reach the US

Mexico's former foreign minister, Jorge Castaneda, has suggested Mexico should play that card, threatening to simply let Central American migrants get through to the US if it does not get what it want on trade issues. Mexico's president, Enrique Pena Nieto himself has said he will "bring all the issues to the table", including "border security".

Those negotiations will likely have an effect not just on Mexico and the United States, but on those coming from Central America hoping to find prosperity, or at least refuge, further north.