Russian and Belarusian citizens who live elsewhere but were accepted through the open registration process will be allowed to run but not under a national flag.

None of the professional or invited athletes set to compete are from Russia or Belarus, according to the Boston Athletic Association (BAA).

The BAA added that it will not recognise the flags or country affiliations of Russian and Belarus until further notice.

The move is in response to the Russian invasion of Ukraine, for which Belarus is providing military support.

"Like so many around the world, we are horrified and outraged by what we have seen and learned from the reporting in Ukraine," BAA President and chief executive Tom Grilk. 

"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."

Ukrainian athletes who can no longer run will be offered a refund or a chance to defer entry until another year, the BAA said.

Athletes from Russia or Belarus no longer eligible to compete will be refunded if sanctions allow.

At least 1,563 civilians have been killed in Ukraine since Russia's ground invasion began on February 24, according to the United Nations.

The true figure is feared to be far higher.

More than 4.2 million Ukrainian refugees have fled the country.

An estimated 15,000 military personnel from both sides have lost their lives and Russia has been accused of committing war crimes, including the murder and torture of civilians in Bucha.

The International Olympic Committee has recommended that International Federations ban Russian and Belarusian athletes outright from their events.

World Athletics is among the governing bodies to have followed this recommendation, with Russian and Belarusian athletes unable to compete in World Athletics events even as neutrals.

The Boston Marathon is due to take place on April 18, returning to its traditional home of Patriots' Day.

It was cancelled in 2020 because of the coronavirus pandemic and raced in October in 2021.