Chinese authorities have formally arrested a prominent scholar of China's Uighur Muslim ethnic group and charged him with separatism, his wife says.
Ilham Tohti, an economics professor in Beijing, has been critical of China's ethnic policies. He has been detained by police since last month.
The US and EU have expressed concern over Mr Tohti's detention.
The Muslim Uighur group mostly live in Xinjiang, in China's far west. There are sporadic clashes in the region.
The government traditionally blames extremists for the violence. Uighur activists, on the other hand, point to ethnic tensions and tight Chinese control as triggers for violence.
Mr Tohti's wife, Guzaili Nu'er, said she received an arrest warrant and notice of the separatism charges on Tuesday. He was being detained in Xinjiang, she added.
She told Reuters news agency the charges were "ridiculous".
"He's never done anything like this. He is a teacher," she said.
Mr Tohti's lawyer, Li Fangping, said he had travelled to Urumqi, Xinjiang's capital, to see his client, but had been denied access so far.
"From my knowledge of him and his statements, nothing constitutes the charge of [inciting] secession," he told AP news agency.
Chinese state media have previously said that Mr Tohti was being investigated for "separatist activities".
Mr Tohti has been critical of China's treatment of the Uighurs and recently expressed fears on his website about increased pressure on the minority group following last October's deadly attack in Beijing's Tiananmen Square.
A car crashed through a crowd and burst into flames, killing five people. Beijing authorities have blamed the incident on Uighur separatists.
Xinjiang has experienced several violent clashes in recent months. According to China state media reports, 11 people were killed in clashes with police earlier this month, while 12 people died in an outbreak of violence in January. Confirming details of these incidents is difficult, because foreign media access to the region is tightly controlled.
China has restricted Mr Tohti's movements on several occasions since deadly ethnic rioting in Urumqi in 2009 that left about 200 people dead.
In January, the US State Department said Mr Tohti's detention appeared "to be part of a disturbing pattern of arrests and detentions of public interest lawyers, Internet activists, journalists, religious leaders and others who peacefully challenge official Chinese policies and actions".