An internal report by the Department of Homeland Security found that President Trump’s proposed wall along the U.S. southern border would take 3.5 years to complete and would cost as much as $21.6 billion, Reuters reported Thursday.

Trump has said he expects the wall to cost $12 billion, while Republicans in Congress pegged the final cost at around $15 billion.

The report looks at the cost and timeline for building a physical barrier of walls and fences along the currently unsecured sections of the U.S.-Mexico border – a little more than 1,250 miles. Homeland Security Secretary John Kelly is set to receive the report in the coming days, according to Reuters.

The cost put forth in the DHS report is much higher than estimates by Trump and GOP congressional leaders, including House Speaker Paul Ryan Paul Davis RyanAt indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates Peterson faces fight of his career in deep-red Minnesota district MORE and Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellSenate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll The Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally MORE.

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Both Kelly and Trump have said that construction on the wall would begin in a matter of months, and have waved off concerns over the project’s price tag. In an interview with Fox News earlier this month, Kelly said he expected funding for the wall to come “relatively quickly.”

“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," he said.

Kelly also said during the interview that he hoped the project would be completed within two years – significantly quicker than the DHS report estimates.

The report also revealed that the government is already working with contractors for the project, and is seeking environmental waivers, Reuters reports.

During his presidential bid, Trump frequently touted plans to construct a massive wall spanning the length of the U.S.-Mexico border, while ultimately having Mexico pay for the project, a claim rejected by Mexico’s President Enrique Peña Nieto.

Trump reaffirmed his commitment to building the wall on Wednesday, telling a meeting of law enforcement officials from the country’s largest cities that he’s already gotten to work on the project.

“The wall is getting designed right now,” he said. “A lot of people say, oh, oh, Trump was only kidding with the wall. I wasn’t kidding. I don’t kid. I don’t kid.”