The cost of sending approximately 5,900 active-duty personnel to the U.S.-Mexico border to provide support to Customs and Border Protection amounts to $72 million, a Pentagon spokesman said Tuesday.

In a statement, Army Col. Rob Manning said the $72 million figure represented "the estimated cost to deploy, operate, sustain, and redeploy forces". He added that "[t]he total cost of the operation has yet to be determined and will depend on the total size, duration, and scope of the DoD support to [the Department of Homeland Security]."

Manning's statement came after The Associated Press reported that the Pentagon had disclosed in a report to Congress that an additional $138 million had been spent on deploying 2,100 National Guard troops who have been performing a separate border mission since April. That would bring the total cost of the two missions to $210 million under current plans, though the total would grow if the active-duty mission is extended beyond the current completion date of Dec. 15.

About 2,800 of the active-duty troops are in South Texas, far from a caravan of Central American migrants in Tijuana, Mexico, south of California. The movement of the migrants into Mexico last month was the stated reason that President Trump ordered the military to provide support for Customs and Border Protection.

Trump, who called the migrant caravan an "invasion," has been accused by critics, including some retired military officers, of using the military deployment as a political tool in the run-up to the Nov. 6 midterm elections.

Sen. Dianne Feinstein, D-Calif., said Tuesday the Pentagon's cost report shows the mission was a "charade."

"These soldiers spent weeks away from home and the Pentagon wasted millions of taxpayer dollars so President Trump could stoke fears of asylum seekers and try to influence election results," she said. "Using our military men and women as political pawns to support an anti-immigrant agenda is a low point, even for this president."

On Tuesday, Trump said he was sure the troops are happy to be on the border mission, even though it means being away from home over Thanksgiving.

"Don't worry about the Thanksgiving. These are tough people," Trump told reporters before flying to Florida for the holiday. "They know what they're doing and they're great and they've done a great job. You're so worried about the Thanksgiving holiday for them. They are so proud to be representing our country on the border where if you look at what's happening, Mexico, the people from Tijuana are saying, wow these are tough people. They're fighting us."

Defense Secretary Jim Mattis has declined to publicly discuss cost estimates for the border mission, saying as recently as last week that he had little confidence in the accuracy of figures he had seen thus far.

"We can estimate costs all we want, I'd prefer to give you real costs. Right now, I can't give that to you," Mattis told reporters last Wednesday when he flew to Texas to see the military's work. "It's the cost of deploying them, it's the cost of transferring their equipment to the border, it's fuel costs, it's all those kinds of costs. So, I just don't want to get into something I can't give you what I believe confidently is accurate."

In its report to Congress on Tuesday, the Pentagon said the estimated $72 million cost includes $19 million for personnel, $20 million for transportation of personnel, equipment and supplies, $28 in operating expenses and $5 million for concertina wire and other border barrier materials.

The report added that as of Nov. 14, about $14 million in actual payments for expenses such as travel, supplies and transportation had been reported by the units involved.

Fox News' Jennifer Griffin and The Associated Press contributed to this report.