President Trump on Wednesday ordered all federal agencies to cut their budgets by 5 percent, catching them unprepared to say in the following days how they would meet his demand.

"I'm going to ask everybody to come back with a 5 percent cut for our next meeting," Trump said in a White House meeting with his Cabinet members. "I think you'll all be able to do it."

Trump made the pledge after a Treasury Department report showed the federal deficit swelling to $779 billion, a $113 billion increase from the prior fiscal year.

Several departments and agencies contacted in the days following Trump’s pledge seemed unprepared for, or even unaware of, Trump’s order to prepare spending cuts for their next White House cabinet meeting. Many declined to provide detail or comment on how they would achieve those cuts, which are unlikely to be implemented since Congress ultimately has the authority to spend money. Some responded with statements on other topics.

[Opinion: President Trump's proposed 5 percent cut to Cabinet agencies won't do much to address deficit: Chart]

The Department of Health and Human Services, for instance, which oversees $1 trillion a year in spending on medical research, food safety programs, drug approvals and programs such as Medicare and Medicaid, responded to an inquiry about the 5 percent cut by touting regulatory relief.

“HHS was the No. 1 cabinet agency in terms of regulatory accomplishments for Fiscal Year 2018, reducing the burden of its regulations in present-value terms by $12.5 billion,” HHS Secretary Alex Azar said.

The agency said its regulatory actions would create a $5.2 billion reduction in spending from 2018 to 2021 at the Centers for Medicare and Medicaid Services.

But HHS would not comment further on planned cost reductions to meet the 5 percent figure.

Other agencies acknowledged the president’s request, but declined to say how they might go about meeting it.

“President Trump has been clear that lowering federal spending is a top priority, and that was the message he reiterated to his Cabinet,” said a spokesman for the Environmental Protection Agency.

Similarly, a spokesman for the Department of Agriculture said that agency “stands with the president and his goal of being fiscally responsible with taxpayer dollars and will absolutely meet his target. When Secretary Perdue was governor of Georgia, five of the eight budgets he submitted were smaller than the previous year’s.”

Meanwhile, a spokesperson for the Department of Housing and Urban Development was not aware of Trump’s promise when asked for comment Friday.

“Let’s see how it plays out when the president’s budget comes out,” said Brian Sullivan, a public affairs specialist at the housing agency. “This aspiration will be expressed in the Fiscal Year [2020] budget.”

Though Trump said he would direct the heads of departments to identify cuts, Sullivan referred a reporter to the Office of Management and Budget, which drafts the president’s budget. OMB did not immediately respond to a request for comment.

Most agencies simply did not respond on the record to requests for comment, including the Departments of Energy, the Interior, Commerce, Labor, and Transportation.

Trump and the Republican-led Congress have increased spending, rather than cutting it. Earlier this year, the administration and Republicans joined with Democrats to increase discretionary spending — the category of spending that Congress authorizes for the agencies each year — by $300 billion in 2018 and 2019.

A 5 percent cut would amount to clawing back around $65 billion of that.

But even that reduction is probably out of reach. Any cuts proposed by agencies would be put into Trump’s fiscal year 2020 budget, and administration officials maintained that Trump wants the reductions included. But past Trump administration budgets have called for steep cuts, only for Congress to increase spending instead. Total discretionary spending, including defense and non-defense, totaled an estimated $1.3 trillion for fiscal year 2018, according to the Congressional Budget Office, up from $1.2 trillion in 2017 and just under $1.2 trillion in 2016.

Discretionary spending, in turn, is a small part of overall government spending, which also includes entitlement spending that occurs automatically, such as Social Security benefits, and interest on the debt. Total spending was about $4.1 trillion for 2018.

That said, some agencies have claimed spending reductions in some areas under Trump. The EPA, for instance, said it cut employees by 6 percent as of January, bringing it in line with staff levels not seen since the Reagan era.

Sean Higgins, Colin Wilhelm, Kimberly Leonard, Robert King, Josh Siegel, and John Siciliano contributed reporting.