A Mexican court on Wednesday freed two migrant rights activists who were arrested on human-trafficking charges last week amid Mexico's ­negotiations to try to avoid US President Donald Trump's threatened tariffs over migration.

A judge in the southern state of Chiapas dismissed all charges against Irineo Mujica and Cristobal Sanchez, activists with the group People Without Borders (Pueblo Sin Fronteras), which has helped organize caravans of Central American ­migrants trekking toward the US.

"We remain very worried by the campaign to criminalize migrants and human rights ­activists under political pressure from the United States government," the group said in a statement.

After being freed, Sanchez said at a press conference that he and Mujica are "the first political prisoners of the 'Fourth Transformation,'" a phrase coined by leftist Mexican President Andres Manuel Lopez Obrador to refer to his plan to radically transform the government.

"The sector that has been hit the hardest by this transformation has been the migrants," said the activist.

"Anyone who assumes a leadership role within a migrant caravan passing through Mexico is singled out, persecuted, imprisoned and subsequently deported," Sanchez added.

Mujica said, "If they continue to invent crimes, if they continue with this corruption, then we don't really have a Fourth Transformation."

Mujica and Sanchez were arrested on June 5, just as a high-level Mexican government delegation was in Washington trying to convince the Trump administration that Mexico is in fact taking strong action to curb the surge of Central 

Americans crossing its territory to the US.

The neighbors reached a deal Friday in which Trump lifted his tariff threat in return for stronger Mexican measures to reduce the flow of migrants.

Under the deal, Mexico agreed to send 6,000 National Guardsmen to reinforce its southern border and expand its policy of taking back asylum-seekers as the US processes their claims.

Trump has warned tariffs will still be on the table if the US deems Mexico's progress insufficient after 45 days.

He is pushing Mexico to accept a so-called Safe Third Country Agreement, in which migrants entering Mexican territory must apply for asylum there rather than in the US.

Lopez Obrador's government faces huge pressure to help curb the exodus of migrants fleeing poverty and violence in Central America's "Northern Triangle" - El Salvador, Guatemala and Honduras - and seeking asylum in the US.

US officials detained or blocked more than 144,000 migrants in May, up 32 percent from April - including 57,000 children.