Defense Secretary Chuck Hagel ordered Wednesday that all U.S. troops who deploy to West Africa as part of the force assisting in the Ebola virus crisis be put in quarantine-like monitoring for 21 days, even though none are expected to treat patients directly.

Hagel’s decision came a day after the Joint Chiefs of Staff recommended such a move. Pentagon officials stopped short of calling it a quarantine, even though troops will be held in “controlled monitoring” before returning home. It began Monday in Italy for an initial group of U.S. soldiers that deployed to Liberia, and is said to include no physical contact with the outside world and those under monitoring eating separately from other service members.

“The fact is, the military will have more Americans in Liberia than any other department,” Hagel said Wednesday at the Washington Ideas Forum, held at the Aspen Institute. “That’s number one. Number two, our people are younger. The cohorts are different. They are not volunteers. And this is also a policy that was discussed in great detail by the communities, by the families of our military men and women. And they very much wanted a safety valve on this.”

Hagel also directed that the military’s top officers to develop a detailed plan in the next 15 days for how the controlled monitoring will be applied. It should take into account the size and scope of the logistics required, said Rear Adm. John Kirby, the Pentagon press secretary.

The joint chiefs also were told to conduct a review of the new regimen within 45 days. At that point, they have to recommend whether the monitoring should continue, based on what is observed among the initial group of troops returning from the mission, known as Operation United Assistance.

“The secretary believes these initial steps are prudent given the large number of military personnel transiting from their home base and West Africa and the unique logistical demands and impact this deployment has on the force,” Kirby said. “The secretary’s highest priority is the safety and security of our men and women in uniform and their families.”

The decision is likely to prove controversial. The Centers for Disease Control and Prevention has  recommended that people at high risk of developing Ebola voluntarily quarantine themselves for 21 days, but it has stopped short of requiring one. State-imposed quarantines for health workers returning from Ebola-affected countries have been challenged, and President Obama criticized them Tuesday, saying that doing so would undermine the broader effort to stop the spread of the deadly virus.

“We don’t just react based on our fears,” Obama said. “We react based on facts and judgment and making smart decisions.”

Hagel’s decision and the recommendation Tuesday from the joint chiefs came after Army Chief of Staff Gen. Raymond T. Odierno ordered on Monday a 21-day “controlled monitoring period” for all redeploying soldiers returning from Operation United Assistance. He said it was a precaution to ensure that soldiers, family members and their communities are confident that all steps necessary are being taken to protect them from the virus.

The military has hundreds of troops in West Africa assisting with the Ebola mission. That number will grow to up to 4,000 in coming days, with most providing transportation, logistics and building treatment units that are desperately needed. No U.S. troops will directly treat Ebola patients, Pentagon officials have stressed.

Obama, asked Wednesday whether he was concerned about there being confusion between quarantine rules used for the military and health-care workers, drew a distinction between the work they will do.

“Well, the military is a different situation, obviously, because they are, first of all, not treating patients,” he said. “Second of all, they are not there voluntarily. It’s part of their mission that’s been assigned to them by their commanders and ultimately by me, the commander in chief. So we don’t expect to have similar rules for our military as we do for civilians. They are already, by definition, if they’re in the military, under more circumscribed conditions.”

This piece was updated with comments from Hagel.