The Pentagon is reviewing how many National Guard, Reserve and Individual Ready Reserve troops to call up in the fight against coronavirus in response to President Donald Trump’s executive order Friday.

Trump ordered Defense Secretary Mark Esper to call up a yet-to-be-determined number of ready reserve components to help in the country’s response to the fast-spreading pandemic.

“This will allow us to mobilize medical disaster emergency response personnel to help wage our battle against the virus,” Trump said in a Friday evening press conference. “We have a lot of people, retirees, great military people, they're coming back in.”

Trump authorized Esper to order units and members of the National Guard and Reserves and some Individual Ready Reserve members to active duty "to augment forces for the effective response to the coronavirus outbreak,” Pentagon spokesman Jonathan Hoffman said in a statement emailed to reporters just after midnight.

“Decisions about which individuals may be activated are still being reviewed.”

The troops will mostly consist of units and personnel with high demand medical capabilities whose call-up would not adversely affect their civilian communities, Hoffman said.

Before calling up National Guard Reserve Component units under this executive order, Esper and the Department of Health and Human Services will first consult with state officials.

Trump’s executive order allows for the call-up of up to a million troops for no longer than 24 consecutive months, but Pentagon officials don’t have a projected number of expected activations, Hoffman said, adding that the Defense Department “is now fully authorized to make activations as needed” and “will provide updates as they become available.”

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The National Guard is already playing a key role in the COVID-19 response.

As of Friday, 12,300 Army National Guard and Air National Guard personnel have been mobilized to help state officials in their coronavirus response plans. And last week, Trump provided federal funds to pay for Guard activation in the three hardest-hit states — California, New York and Washington.

It is a move Guard officials say will both speed up mobilizations by taking the financial burden off governors and provide better benefits for the troops.

play_circle_filled Latest Guard update: More than 12,300 troops mobilized for COVID-19 response Every state, three territories and Washington D.C. have activated Army and Air National Guard personnel to assist in efforts to combat the spread of COVID-19.

More than 100,000 individuals across America have tested positive for coronavirus, and more than 1,200 deaths have been attributed to the illness. The virus has forced worldwide closures of businesses and resulted in the self-quarantining of much of the world’s population in recent weeks.

Trump said that numerous military retirees have already volunteered to assist with medical response efforts, but the additional order is needed to fill gaps.

Earlier Friday, Army officials said that more than 9,000 former soldiers with medical training expressed interest in assisting with the coronavirus pandemic efforts. The Army emailed more than 800,000 such troops to gauge their interest.

Also on Friday, Trump signed into law a $2 trillion economic stimulus package related to the coronavirus outbreak that includes more than $10 billion in emergency funds for the Defense Department.

The executive order authorizes Defense Secretary Mark Esper and acting Homeland Security Secretary Chad Wolf to coordinate with state governors to ensure the reserve activations do not interfere with any of those missions.

The military reserve components include several different categories of veterans and part-time service members. The selected reserve, some of whom have already been activated, regularly train for a variety of military and community response missions.

The Individual Ready Reserve is made up mostly of individuals who have already served in an active-duty component and still have some military service obligation remaining. Under federal law, they can be involuntarily recalled during a national emergency.

Pentagon officials did not immediately provide any guidance on the recall order.

Reporter Meghann Myers contributed to this story.

This is a developing story. Please stay with MilitaryTimes.com for updates.