Gen. Jack Kelly, the Homeland Security Secretary, testifies before the Senate Homeland Security and Governmental Affairs Committee. (Screen grab from C-SPAN)

(CNSNews.com) - Gen. John Kelly, the secretary of homeland security, told Congress on Wednesday there's "no way" he can estimate how much President Trump’s long-promised border wall will cost.

"I mean, I don't know what it will be made of; I don't know how high it will be; I don't know if it's going to have solar panels on the side, what one side's going to look like and how it's going to be painted -- I have no idea. So I can't give you any type of an estimate.

I will say this, that it's unlikely that we will build a wall, or a physical barrier, from sea to shining sea, but it is very likely -- I'm committed to putting it where the men and women (Border Patrol) say we should put it."

Kelly said a "physical barrier works" in the 650 miles where it currently exists along the southern border.

He said there are other places along the border where a physical barrier would also work, primarily to deflect the flow of people away from cities, where it is more difficult to detain people coming into the U.S. illegally.

"The barriers work. Technology also works. But all of it doesn't work at all unless you have men and women who are willing to patrol the border, develop relationships which they do with their Mexican counterparts directly across the border."

Kelly said he will put walls and other barriers in those areas where his Border Patrol agents tell him it is needed. He said their input will be integral to the process.

‘Embarrassing’

Sen. Claire McCaskill (D-Mo.) asked Kelly if President Trump is okay with fencing instead of a solid wall.

“The president has told me, Kelly go do it. We need to protect the Southwest border in any way that that makes sense. I have a lot of elbow room," he added.

"So he knows that we're not going to build a... 2,000 mile concrete wall. The president knows that, right?” McCaskill asked Kelly.

“The president knows that I’m looking at every variation on the theme, and I have no doubt when I go back to him and say, you know, Boss, a wall makes sense here; high-tech fencing makes sense over here; technology makes sense over here -- I have no doubt that he will go tell me to do it."

McCaskill called it “embarrassing” that Trump is insisting on a border wall that Mexico will pay for.

“It's not going to happen,” she said. “Everybody in Congress knows it's not going to happen. Every Republican knows it. Every Democrat knows it. It appears the only person who won't say it out loud is the president of the United States. It's embarrassing."

McCaskill said it does no good to build a big wall if it limits the "situational awareness" of border patrol agents who can't see what's happening on the other side.

She urged Kelly to "Speak truth to power."