Amid intensifying scrutiny of the Senate Republican proposal to spend up to $1 billion on security for the new White House ballroom, top Department of Homeland Security and U.S. Secret Service officials say the money would also be spent on “other critical missions.”

Those missions, they said, would include securing “frequently visited venues” outside of the White House. 

In a letter to congressional leaders obtained by ABC News, Homeland Security Secretary Markwayne Mullin and Secret Service Director Sean Curran described the proposed billion-dollar package as “critical funding to address urgent needs in response to the unprecedented increase in threats against the President and other public officials.”

Mullin and Curran said that the shooting at the White House Correspondents’ Association Dinner last month as well as a shooting near the National Mall earlier this week show a need for a secure White House ballroom.

The letter said the security upgrades to the “East Wing Modernization Project” will “afford needed protection for the President, his family, and visitors, along with the below-ground security functions.”

The officials noted that, per the text of the Senate reconciliation bill, “none of these funds will be used to support non-security improvements at the White House.”

The Senate proposal, released earlier this week, would provide $1 billion for the Secret Service “for the purposes of security adjustments and upgrades, including within the perimeter fence of the White House Compound to support enhancements by the United States Secret Service relating to the East Wing Modernization Project.” 

Without spelling out how much of the billion dollars would be spent on the ballroom construction project specifically, the officials said the funding would also be directed toward other locations, including “frequently visited venues facing heightened risk due to their public visibility and static nature.”

The text of the Senate’s bill makes no reference to “frequently visited venues” outside of the White House that Mullin and Curran mentioned in their letter.

Also, Mullin and Curran said the additional money would also go toward training USSS agents, USSS training facilities, the Secret Service’s Special Operations Division’s work on drones and biological and “other emerging threats,” as well as securing “high profile national events that require significant planning.”

Overall, the $1 billion package is described in the letter as a “critical infusion to ensure the safety of the current President and future Presidents.”

​By comparison, ​to fund all of its operations, USSS receives more than $3 billion a year from Congress via the regular appropriations process.