Boston Marathon organizers have banned Russian and Belarusian athletes from taking part in this year's event over Moscow's invasion of Ukraine.

Runners who were accepted via open registration to the Boston Marathon and reside in their home countries Russia and Belarus will not be allowed to compete, the Boston Athletic Association (BAA) said Wednesday.

However, Russian and Belarusian citizens residing outside either country will be permitted to compete but not under their respective flags.

The restrictions, which also apply to the 5K race, are the latest in a series of sanctions across global sport in response to Russia's invasion of Ukraine.

Belarus, a key staging area for the invasion, has faced broad punishments as well.

"We are horrified and outraged by what we have seen and learned from the reporting in Ukraine," BAA President and CEO Tom Grilk said in a statement.

"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 not recognize country affiliation or the flag of Russia or Belarus at any of its races and events "until further notice."

The annual road race is the world's oldest marathon and one of six that comprise the prestigious World Marathon Majors, attracting some of the world's top runners.

This year's race is set for April 18.