The Boy Scouts of America announced on Monday that they would begin accepting transgender boys, in a move that has upset many conservatives. 

"Starting today, we will accept and register youth in the Cub and Boy Scout programs based on the gender identity indicated on the application," said Boy Scouts of America communications director Effie Delimarkos in an emailed statement.

Delimarkos explained the change by citing increasingly fluid definitions of gender under state laws, which can "vary widely from state to state". The Cub and Boy Scouts programs will still be aimed at boys, but the change will allow children to apply even if they are not categorised as male on their birth certificate.

"The BSA is committed to identifying program options that will help us truly serve the whole family," the Scouts said.

The decision has been met largely with applause from progressive groups and disappointment from conservatives.

Advocacy group Scouts for Equality said: "This is another historic day for the Boy Scouts of America. The decision to allow transgender boys to participate in the Cub Scouts and the Boy Scouts is an important step forward for this American institution."

Jonathan Greenblatt, chief executive of the Anti-Defamation League, applauded the move. He said: "No one should be denied the opportunity to participate in any Boy Scout troop because of their gender identity or expression."

But many conservatives see it as further rejection of the Boy Scouts' traditional foundations. Southern Baptist Russell Moore, president of the Ethics & Religious Liberty Commission, said: "Now we see once again that the Boy Scouts really is committed to a gender-theory culture war that evangelical Christians and many other Americans just can't accept.

"I think, for some, this will be the final sign that it's time to go," he told the New York Times.

"The Boy Scouts of America sacrificed its last vestige of integrity on the altar of political correctness," wrote Todd Starnes for Fox News. He described the move as a "complete capitulation to the gender and sex revolutionaries."

For conservatives who now feel disenfranchised, alternative groups do exist. Starnes for example recommends Trail Life USA, a "Christ-centered scouting program" that began in 2014 and now has nearly 30,000 members. The group was founded by former Scoutmaster John Stemberger, after the B.S.A decided to allow gay members in 2013.

In response to the B.S.A's recent statement, Stemberger said: "It's the beginning of the end of what the Boy Scouts used to mean. It's really a sad move."

Stemberger warned of child protection risks, and said that the decision will "put boys in a state of confusion and does nothing to help normal psychological development."

The Boy Scouts of America states its mission as preparing youth for life and leadership. The group has nearly 2.3 million members between the ages of 7 and 21 and roughly 960,000 volunteers in local councils throughout the country, according to its website. Many scout groups are sponsored by conservative groups, who may withdraw their support following the BSA announcement. 

Additional reporting by Reuters