Moscow (AFP) - Russia is moving US basketball star Brittney Griner to a penal colony after she lost an appeal against a drug conviction, her lawyers said Wednesday, drawing a sharp rebuke from the White House.

Griner, who has been jailed for nine years for possession of a small quantity of cannabis oil, was transferred out of a detention centre on November 4, her legal team said.

She "is now on her way to a penal colony," lawyers Maria Blagovolina and Alexander Boykov said in a statement.

"We do not have any information on her exact current location or her final destination," they added.

Russia generally notifies of a prisoner's transfer to a different address by mail, taking up to two weeks, the lawyers said.

Griner's case has drawn outrage in the United States, with Secretary of State Antony Blinken seeking a deal with Russia to free her despite soaring tensions over Moscow's offensive in Ukraine.

White House Press Secretary Karine Jean-Pierre reiterated that the United States had put forward a "substantial offer" to Russia to resolve her case.

'Wrongful detention'

"Every minute that Brittney Griner must endure wrongful detention in Russia is a minute too long," 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, a two-time Olympic basketball gold medallist and Women's NBA champion, had been in Russia to play for the professional Yekaterinburg team during her off-season from the Phoenix Mercury Women's National Basketball Association side.

She said the cannabis in vape cartridges was to treat pain from her sporting injuries, but Russia does not allow medical marijuana use.

Observers have suggested that Griner and another American jailed in Russia, Paul Whelan -- a retired US Marine arrested in December 2018 and accused of spying -- could be traded for Viktor Bout, a famed Russian arms trafficker serving 25 years in prison on a 2012 conviction.

Prisoners' rights activist Vladimir Osechkin said conditions in penal colonies are much harsher than in detention centres. 

"It is a more totalitarian system with Gulag uniforms and 100 people per room in barracks," Osechkin, who founded the Gulagu.net rights group, told AFP, warning that prison officials routinely orchestrate conflicts and fights between inmates. 

"If the Kremlin decides not to torture the basketball player and creates VIP conditions for her, she will be allowed to eat separately, play sports and keep fit," said Osechkin.

"But if a decision is made and the federal prison service receives an order to put pressure on her then of course her life and health will be in danger."

Activists say abuse and torture are frequent in Russia's vast network of prisons run by the Federal Penitentiary Service (FSIN), a successor to the notorious Gulag system of the Stalin era.

Penal colonies are the most common type of prisons and are known for their harsh treatment of inmates, unsanitary conditions and lack of access to proper healthcare.

Prison officials also often limit inmates' contact with lawyers and family. Harassment of prisoners sometimes leads to prison riots.

A number of US citizens including Whelan are currently behind bars in Russia. 

Whelan's brother David regularly describes Paul's life in the IK-17 colony in the central region of Mordovia, saying he has undergone sleep deprivation and that suicides are common in prisons.

The treatment of the jailed opposition leader Alexei Navalny has also highlighted abuses in prisons, activists say.

The 46-year-old has been repeatedly placed in solitary confinement, which his supporters say amounts to torture.

Anti-torture project Gulagu.net has drawn attention to what it calls systemic abuse and sexual violence towards prisoners.

Last year it released harrowing video footage of a naked man being raped with what appeared to be a broom stick at a prison hospital.