Secretary of Homeland Security Kirstjen Nielsen speaks to George Washington University's Center for Cyber and Homeland Security, in Washington, Wednesday, Sept. 5, 2018. Nielsen lays out her vision for the sprawling department, as midterm elections l
Secretary of Homeland Security Kirstjen Nielsen speaks to George Washington University's Center for Cyber and Homeland Security, in Washington, Wednesday, Sept. 5, 2018. Nielsen lays out her vision for the sprawling department, as midterm elections l

U.S. Homeland Security chief Kirstjen Nielsen had a blunt message Sunday to a migrant caravan slowing moving north through Mexico toward the United States: "Do not come."

She told Fox News, "There's a right and legal way to enter this country," by filing U.S. asylum claims while they are in Mexico. "This is about the rule of law."

Nielsen said, "We have a crisis on the border," with U.S. officials apprehending 1,500 to 1,700 migrants a day as they cross into the United States.
 
She offered her assessment as Defense Secretary Jim Mattis told reporters traveling with him on a trip to Prague that Pentagon officials are working out details on the the deployment of several hundred troops to the southern U.S. border.

U.S. Department of Homeland Security Secretary Kir
U.S. Department of Homeland Security Secretary Kirstjen Nielsen visits U.S. President Donald Trump's border wall in the El Centro Sector in Calexico, California, Oct. 26, 2018.

On Friday, the Pentagon approved a request by the Department of Homeland Security to send the troops to the U.S.-Mexico border in what is described as a support role. A statement said personnel will support the border patrol with planning assistance, medical teams and the construction of temporary housing, along with other support duties.

FILE -A Customs and Border Protection vehicle patr
FILE - In this July 24, 2014, photo, a Customs and Border Protection vehicle patrols on the Texas border near the Rio Grande in Mission, Texas.

They will join more than 2,000 members of the National Guard already deployed to the area who are providing support for border patrol agents.

Meanwhile, the Trump administration is reported to be considering a new executive order aimed at blocking asylum seekers and immigrants from crossing the U.S.-Mexico border.
 

Members of a U.S.-bound migrant caravan cross a br
FILE - Members of a U.S.-bound migrant caravan cross a bridge between the Mexican states of Chiapas and Oaxaca after federal police briefly blocked them outside the town of Arriaga, Oct. 27, 2018.

News reports quoting unnamed administration officials say authorities are weighing a range of administrative and legal actions on grounds of national security to restrict the ability of migrants to seek asylum.
 
Although no decision has reportedly been made yet, immigration attorneys told VOA the move would be quickly challenged in court.
 
The caravan of migrants from Honduras and Guatemala, making its way north on foot, is still hundreds of kilometers away from the closest U.S. border.

Honduran migrants take part in a caravan heading t
Honduran migrants take part in a caravan heading to the US on the road linking Ciudad Hidalgo and Tapachula, Chiapas state, Mexico, Oct. 21, 2018.

The U.N. refugee agency is urging Washington to allow people fleeing persecution and violence, including those who are traveling with the Central American caravan, to request asylum on U.S. territory.  

“Our position globally is that the individuals who are fleeing persecution and violence need to be given access to territory and protection including refugee status and determination procedure," UNHCR spokesman Andrej Mahecic told VOA.  "And, if the people who are fleeing persecution and violence enter Mexico, they need to be provided access to the Mexican asylum system and those entering the United States need to be provided access to the American asylum system.”   

Most of those traveling north are from Honduras. There has been no evidence to back up President Donald Trump's claim last week that "Middle Easterners" are also with the group.

Lisa Schlein and Aline Barros contributed to this report.