Mexico's top diplomat said Wednesday he received assurances from Homeland Security Secretary Kirstjen NielsenKirstjen Michele NielsenEx-Trump official: 'No. 1 national security threat I've ever seen' is GOP Left-leaning group to track which companies hire former top Trump aides Rosenstein: Zero tolerance immigration policy 'never should have been proposed or implemented' MORE that National Guard troops deployed to the border will only act in a supporting role.
Foreign Relations Secretary Luis Videgaray Caso said on Twitter that Nielsen "clarified some aspects of the deployment" over the phone.
According to a Foreign Relations Secretariat press release, Nielsen said the troops will be unarmed and not directly engage in immigration or customs controls.
Nielsen said the new deployment would be similar to earlier National Guard deployments along the border, Operation Jump Start, in 2006, and Operation Phalanx, in 2010, according to Mexican diplomats.
But Mexico also warned that a militarization of the region could have severe consequences.
"In all communications on the issue, the government of Mexico has expressed to the government of the United States that, if the announced deployment of the National Guard were to translate into a militarization of the border, that would gravely damage the bilateral relations," read the release.
The National Guard is restricted by law from performing tasks attributed to Customs and Border Protection and Border Patrol officers.
President TrumpDonald TrumpKinzinger says Trump 'winning' because so many Republicans 'have remained silent' Our remote warfare counterterrorism strategy is more risk than reward Far-right rally draws small crowd, large police presence at Capitol MORE signed Wednesday a proclamation to deploy the National Guard to the border.
"Until we can have a wall and proper security, we are going to be guarding our border with the military," he said Tuesday.
In an interview on "Fox & Friends" Thursday, Nielsen said previous similar operations had been successful by providing logistical support to Department of Homeland Security officers.
"Operation Phalanx, as you know, was a way the National Guard could provide air support. We would look for them to do that. They provide medical care for those we interdict. They help us do fleet maintenance; we need a lot of mechanics in that terrain," she said.
"It's a lot of support functions that will free up the border patrol to do what they do best," added Nielsen.
But asked about legal limitations that prevent National Guard troops from conducting arrests, seizures and interdictions, Nielsen indicated she'd look to Congress to change those laws.
"We are looking in every way we can act within the executive branch but I really will continue to ask Congress to please work with me in the next couple months to pass legislation. Some of the [limitations] are absolutely the result of loopholes in our system. They were probably never meant to be there," she said.