EXCLUSIVE: In his first television interview as Homeland Security secretary, retired four-star Marine Gen. John F. Kelly told Fox News he wants the U.S.-Mexico border wall finished in two years – setting an ambitious schedule for the project ordered last week by President Trump.

"The wall will be built where it's needed first, and then it will be filled in. That's the way I look at it," Kelly said. "I really hope to have it done within the next two years."

Fox News traveled with Kelly in McAllen, Texas, on Wednesday where he saw first-hand the challenges for Border Patrol agents. The Rio Grande Valley, known as the "RGV sector," is among the busiest. On any given day, Border Patrol agents pick up at least 600 people who have crossed the Mexican border, entering the U.S. illegally.

Those personnel, he explained, are all part of the broader plan for securing the border.

"Any discussion about the protection of our southwest border involves discussion of physical barriers but also of technological sensors, things like that,” he said. “But it's a layered approach, and it’s got to be backed up by great men and women who are going to make sure that the wall is intact."

But first, the department faces the tough task of funding – and then building – what would be the largest-ever construction project undertaken by the president who made his name in real estate.

Kelly, who was tasked by the president’s executive order with overseeing the planning and construction of the wall, echoed Trump in saying they already “have the authority” under existing law.

“We're looking at the money aspect,” he acknowledged. But he said the White House is working with Congress on the timetable.

“I think the funding will come relatively quickly and like I said, we will build it where it's needed first as identified by the men and women who work the border," Kelly emphasized.

Kelly said it will be only a matter of months before construction begins.

Kelly also said he supported a "surge" of resources to the border so that processing those who cross illegally can happen in a matter of weeks, not "600 plus days."

"If we could surge the court proceedings -- immigration court proceedings on the border -- and within the law, do it very rapidly ... I think that alone would act as a huge deterrent for people who are considering making the trip up," he said.

As for hostility to the wall from Mexico, Kelly said the safety of Americans comes first, though he wants to build a partnership on shared border issues. "I'd really like to establish a relationship on this, on the other side. It would be a mutually beneficial relationship."

Kelly also defended his agents in the wake of last week’s controversial executive order suspending the refugee program and restricting travel from seven mostly Muslim countries. As his agency came under fire over the weekend, he said the department worked to verify reports of mistreatment, and could not. Kelly suggested critics had blown the issue out of proportion.

"Mr. Trump is not loved by everyone in America, and I think this very rapid succession of decisions, I don't think the American public is really all that used to people making decisions,” he said. “I really don't think they're used to people that say things on the campaign trail actually turning them into action."

Asked if the pace had come as a "shock" to the public, Kelly said: "Yes, I think so. But I will tell you the men and women of Homeland Security did a great job out on the front lines, in this case mostly at the airports. People were treated with dignity and respect."

Kelly knocked down media reports that he first learned of the executive order by watching television, the day it was signed, a story first reported by the New York Times: "As soon as I was confirmed which was on Friday a couple of weeks ago, inauguration day, I knew that they were being developed.”

Asked if he was "blindsided by the order," Kelly said, "Not at all. I saw the initial couple of cuts on them probably on Tuesday maybe Thursday, knew it was coming soon and then it came. "

After more than 45 years of service, Kelly retired last year, and did not plan a return to Washington or full-time employment. He said it all changed with a cold call from the transition team when he and his wife Karen were relaxing.

Kelly was initially skeptical about the caller, who is now White House chief of staff.

"We were sitting on the couch when I got the original call on a Saturday afternoon and Reince Priebus called me,” he said. “I don't know him. Once he convinced me it was really Reince Priebus, he said, ‘Would you come up and talk to Mr. Trump, he'd like to talk to you about a position in the administration.’ And I said, ‘I can do that, I'll be up tomorrow.’”

He told his wife he thought the Trump administration was about to offer him a job.

“She said, ‘take it, your whole life, our whole life, the Kelly family is a life of service.’"