Homeland Security Secretary Kirstjen Nielsen said "everything is on the table" with regard to border security during the unveiling of a border wall project in California on Friday.

Nielsen's remarks came as the Trump administration considers ways to slow immigration at the U.S.-Mexico border and as a caravan of migrants -- mostly made up of thousands fleeing violence and poverty in Central America -- are making their way north through Mexico.

The caravan covered more than 60 miles Friday and was roughly 990 miles from McAllen, Texas, and over 2,300 miles from San Diego.

"We are looking at every possible way within the legal construct that we have to make sure that those who don't have the legal right to come to this country do not come in," Nielsen said from the El Centro Sector near Calexico in front of a newly constructed 30-foot, two-mile fence.

"Looking at this, I would not attempt to climb it," she added.

In an effort to enhance security, the Pentagon recently approved a request for 800 additional troops at the southern border. The White House is looking at other measures, including blocking migrants from seeking asylum in the U.S., which would almost assuredly result in court challenges.

Around 2,000 National Guard troops already serve on the border. The additional troops ordered will operate in areas in California, Arizona and Texas from next Tuesday until Dec. 15, a Pentagon official said.

They will not be authorized to detain migrants. Instead, they will assist Border Patrol personnel on erecting barricades and fencing, conducting helicopter and airplane transport and providing assistance to medical teams and patients.

But the Trump administration's policies have drawn sharp criticism from advocates for immigrants. The efforts to curtail migrants seeking asylum could have "disastrous practical implications for our asylum obligations, for our moral and legal obligations," said Andrea Guerrero, executive director Alliance San Diego.

"We know that civil rights attorneys are preparing to litigate right now," she said. "They're preparing to litigate right away. I don't know if (Trump) cares if he wins the litigation. He wants to score political points ... it's all part of the same political ploy to stoke fear for political reasons and build more walls."

The two-mile section of fencing will go a long way in keeping immigrants out of the country, Nielsen said.

"Let me be clear: Walls work," Nielsen said.

In March, Trump hailed the project in Calexico as the start of his proposed border wall -- the central promise of his 2016 presidential campaign, the Hill reported.

In the leadup to the midterm elections, Trump has focused on immigration issues and the approaching caravan.

"I called up the military," Trump said Friday at a meeting of young black conservative leaders. "We're not letting them in, they ought to go back now because we're not."

The Associated Press contributed to this report.