The Government Accountability Office (GAO) on Monday said the Trump administration had not provided a full analysis of the costs for its proposed U.S.-Mexico border wall.

Failure to provide that information could make it hard to track costs or performance for a project expected to cost billions of dollars, the GAO said in its report.

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The government watchdog released a report on Monday claiming the Department of Homeland Security has not produced comprehensive plans for the costs and location of the border wall, which poses "an increased risk that the Border Wall System Program will cost more than projected, take longer than planned, or not fully perform as expected."

The GAO report was commissioned in order to assess the Trump administration's progress on the president's plan to build a wall at the southern border, a proposal that became a rallying cry for his supporters during the 2016 presidential campaign.

A House homeland security spending bill released last month offers $5 billion to build the wall, while its version in the Senate allots $1.6 billion.

Trump has warned he might shut down the government in the fall if he does not get more than the Senate's proposal.

The GAO report notes there have been fences and walls at the U.S.-Mexico border since the 1990s, but tracks the additions that have been proposed or added since 2017.

The report recommends that Homeland Security analyze future costs of additions to the wall and says that the department has agreed to do so.

U.S. Customs and Border Protection has tested eight prototypes when considering designs for border barriers, the report notes, assessing each for security and costs. Four of the prototypes are made of concrete.

Trump's immigration policies have undergone greater public scrutiny since reports emerged in recent months that his hard-line "zero tolerance" policy resulted in the separation of more than 2,500 children from their parents while the adults await prosecution for illegally crossing the border.