border wall
An internal Homeland Security report estimates President Trump's proposed wall along the U.S. border with Mexico could cost $21.6 billion. Above, a view of the fence at El Paso, Texas, Feb. 2, 2017. Jose Luis Gonzalez/Reuters

President Donald Trump’s “big, beautiful wall” along the 1,250-mile U.S. border with Mexico will cost an estimated $21.6 billion, an internal Homeland Security report estimates.

Reuters reported Thursday the internal report, which assumes funding will come from Congress this spring, puts the price tag $12 billion higher than Trump estimated during his campaign and $15 billion higher than House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell have estimated.

Reuters said Homeland Security Secretary John Kelly is likely to get the report in coming days.

The report does not account for funding constraints or legal battles that are likely to crop up.

About half of the border already is fortified and the new construction would extend the barrier to cover the gaps.

The report recommends construction begin with 26 miles of border near San Diego, El Paso, Texas, and in the Rio Grande Valley at a cost of $360 million and commence in September.

The rest of the construction is expected to be much more costly. Much of the land is privately owned, and costs could go as high as $15 million per mile in areas involving waters shared by the U.S. and Mexico.

The second phase would cover 151 miles in the Rio Grande Valley; Laredo, Texas; Tucson, and El Paso and Big Bend, Texas. The third phase would cover the remaining 1,080 miles.

Trump has recommended that Congress put up the money for the wall so construction can begin without delay. He has repeatedly said Mexico will reimburse taxpayers, and Mexico repeatedly denied it will do so.

"We intend to address the wall issue ourselves," Senate Majority Leader Mitch McConnell, R-Ky., told reporters two weeks ago.

Reuters said the report indicates the government already is seeking waivers to address environmental restrictions in some areas, and existing contractors already are planning steel purchases for the project.

Trump said Wednesday design efforts already are underway.

Trump has proposed a 20 percent import tax on products from Mexico to fund the wall, which would raise the price of everything from fruits and vegetables to the family car.