The Boston Athletic Association announced Wednesday it will bar Russian and Belarusian registrants who live in those countries from running in the Boston Marathon and BAA 5K.

The policy will not affect citizens who are not residents of those countries, but they will not be permitted to race under their flags, which the BAA said it will not recognize until further notice.

The ban will impact 63 runners between the Marathon and 5K.

“Like so many around the world, we are horrified and outraged by what we have seen and learned from the reporting in Ukraine,” B.A.A. president and CEO Tom Grilk said in a press release. “We believe that running is a global sport, and as such, we must do what we can to show our support to the people of Ukraine.”

The BAA said it will make "reasonable" attempts to deliver refunds to the runners who won't be able to participate under the new guidance, but will only do so within the bounds of federal and international sanctions.

It’s not the first step the marathon organizers have taken in response to Russia’s invasion of Ukraine. At the end of February, the nonprofit offered to refund Ukrainians who had registered for the 2022 races, or let them defer to a future year.