The price tag for keeping the National Guard in Washington D.C. since Jan. 6 has reached an estimated $438 million, a senior defense official told Fox News.

The estimate came as the nation came close to a month since the riots that left rocked the U.S. Capitol. Chief Pentagon spokesman John Kirby recently said that Defense Secretary Lloyd Austin had committed to ordering all units to "stand down" in the next 60 days.

Between 5,000 to 7,000 troops are staying in D.C. until mid-March, a significant reduction from the 26,000 that were deployed to help secure the inauguration.

A spokesman previously confirmed to Fox News that the D.C. National Guard would "remain on orders until March 31, 2021."

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Acting Army Secretary John E. Whitley said at the end of last month that the Guard had received requests for follow-on assistance from the U.S. Secret Service and other law enforcement entities in D.C.

"National Guard members will be postured to meet the requirements of the supported civil authorities up to and including protective equipment and arming if necessary," Whitley said at the time. 

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The continued presence of the Guard has provoked criticism from some.

"The lesson of the Capitol riot is not that we should quarter a standing army at the Capitol just in case, but rather that our security measures should be calibrated to the actual threats," Sen. Tom Cotton, R-Ark., said at the end of last month.

The Associated Press, Fox News' Caitlin McFall, and Lucas Tomlinson contributed to this report.