President Donald Trump's "wall" along the U.S.-Mexico border will be a series of fences and walls that would cost as much as $21.6 billion, and take more than three years to construct, based on a U.S. Department of Homeland Security (DHS) internal report seen Thursday.

The report's estimated price-tag is much higher than a $12 billion figure cited by Trump in his campaign and estimates as high as $15 billion from Republican House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell.

The report is expected to be presented to DHS Secretary John Kelly in the coming days, although the administration will not necessarily take actions it recommends.