Acting Defense Secretary Patrick Shanahan has approved a Department of Homeland Security request to send approximately 320 troops to provide additional support along the U.S.-Mexico border, the Pentagon announced Monday evening.

Pentagon spokesman Lt. Col. Jamie Davis said the troops' duties will include driving Customs and Border Protection (CBP) vehicles to transport migrants and monitoring the condition of migrants in CBP custody. Department of Defense lawyers will also be on hand to help Immigration and Customs Enforcement (ICE) process the migrants.

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"DoD personnel will not perform any law enforcement functions," Davis said in a statement. "In any situation that requires DoD personnel to be in proximity to migrants, DHS law enforcement personnel will be present to conduct all custodial and law enforcement functions, and provide force protection of military personnel."

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Davis said the extra troop support will cost about $7.4 million through Sept. 30.

The decision provides approval for a plan the Pentagon disclosed last Friday. There currently are about 2,900 active-duty troops operating in support of DHS at the border, plus about 2,000 National Guard troops. A key aspect of the policy governing military involvement at the border has been a prohibition on direct contact with migrants.

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