A senior Afghan official says he was violently kidnapped and sexually molested on the orders of Vice-President Abdul Rashid Dostum.
The accusation came from Ahmad Eshchi, the former governor of General Dostum's home province of Jowzjan in the north.
He said the vice-president and 10 other men assaulted him while he was forcibly kept at the former warlord's residence for five days late last month.
Gen Dostum denied the accusation, describing it as a "provocation".
He said Mr Eshchi was detained not by him, but by the country's intelligence service.
"He (Eshchi) was detained by Afghan security forces for allegations of funding the opposition and having a hand in repeated security issues," a spokesperson for Gen Dostum said in a statement.
"For some time there has been a destructive movement by some unknown circles against the First Vice President," it added.
Gen Dostum is an ethnic Uzbek and a former warlord blamed for some of the worst atrocities in Afghanistan's long-running civil war. He joined the country's national unity government in 2014.
Mr Eshchi described the alleged abuse, which he said began with his kidnap on 24 November, in graphic detail, although his account cannot be independently verified.
He said that the abduction took place after a public game of buzkashi, a sport where players on horses attempt to put the carcass of a goat in a goal, between his and General Dostum's team.
"(Gen) Dostum pushed me on the ground, pressed his leg on my throat and abused me. Then he [took] me to his house. When I arrived [at] his house, he shouted [at] his guards to bring me out of the car," he told BBC Afghan.
"He ordered his eight guards to undress me. They even [pulled] off my trousers."
He said he was eventually transferred to the Afghan security service office and then released.
The office of Afghan President Ashraf Ghani promised a thorough investigation into the accusations.
When the former warlord joined Mr Ghani's ticket in 2014, it was seen as a controversial move but one that could signal some kind of reconciliation with his ability to secure the confidence of the Uzbek minority.
"For the Afghan government nobody is above the law. Rule of law and accountability begins in the government itself and we are committed to it," said Afghan presidential spokesman Haroon Chakhansori.
Both the European Union and the United States called for an investigation into the reported mistreatment of the former governor, who only re-emerged on Saturday after disappearing for two weeks.
"The unlawful detention and reported mistreatment... raises serious concerns," the US Embassy said in a statement.
"We would welcome the Afghan government's move to swiftly investigate these allegations."