BG's move from the detention center in Iksha began on Friday ... which happened to be one day after she met with U.S. embassy officials.

It's something Griner's family and team have feared ever since her conviction in August ... as a penal colony is far worse than a detention center. Prisoners are forced to perform labor, and it's much more difficult to make contact to the outside world.

Griner's team was not made aware of the update until Tuesday ... and her current location is unclear. Her legal team says it may take up to two weeks to be notified of her destination.

Lindsay Colas, Griner's agent, released a statement saying the number one concern is her client's health and well-being.

Colas says Griner's camp continues to work with the U.S. government in an effort to bring her home and keep her safe in the meantime.

"We are thankful for everyone's support, and hope that as we near nine months of detention, that BG and all wrongfully detained Americans will be shown mercy and returned home to their families for the holidays," Colas said.

The White House also released a statement ... slamming the move.

"Every minute that Brittney Griner must endure wrongful detention in Russia is a minute too long," White House Press Secretary Karine Jean-Pierre said.

"As the Administration continues to work tirelessly to secure her release, the President has directed the Administration to prevail on her Russian captors to improve her treatment and the conditions she may be forced to endure in a penal colony."

Griner has been in custody in Russia since February ... after she was accused of bringing hashish oil in her luggage at a Moscow airport.

She pleaded guilty to drug charges in July ... and was sentenced to 9 years in prison.

Griner spent her 32nd birthday behind bars last month ... and her appeal was denied on October 25.