Senate Armed Services Committee Chairman John McCain is demanding the Department of Homeland Security request military help to combat drug trafficking and illegal immigration on the Mexican border.

In a letter to Homeland Security Secretary Jeh Johnson, McCain, R-Ariz., called on him to immediately request Department of Defense support "so we can take full advantage of the department's air assets to secure the border and combat illicit drug trafficking."

McCain said Army drones are flying along the Mexican border, but none of the training missions are coordinated with DHS to help detect drug smuggling.

McCain said the Defense Department can participate in helping federal law enforcement stop drug trafficking "including but not limited to, aerial reconnaissance along the international border."

But the military cannot step in without a request from Johnson.

"It is my understanding you have made no such request to DOD," McCain wrote to Johnson.

McCain listed four questions in his letter, including a query as to whether DHS coordination with the military would "increase or decrease DHS's situational awareness of drug trafficking along the U.S.-Mexico border."

Read the letter here:

McCain Letter