(adds foreign ministry, video of sentencing)
By Megha Rajagopalan
BEIJING, June 17 (Reuters) - Concerns about the prolonged detention in China of prominent Uighur academic Ilham Tohti are rising amid a crackdown by Beijing on Islamist separatists it says are seeking to establish an independent state in the far west.
Tohti's lawyer said on Tuesday that sources have told him that the Minzu University economics professor, who was detained in January and later charged with separatism, may have been secretly tried and given a heavy jail sentence.
Li Fangping said police wouldn't say whether a secret trial had taken place. Calls by Reuters to police in Urumqi, the capital of Xinjiang region, went unanswered. China's Ministry of Foreign Affairs declined to comment on Tohti's case.
"Someone finally picked up the phone at the Urumqi public security bureau late yesterday," Li said. "They didn't confirm or deny that a trial had taken place."
Tohti's case underscores the government's crackdown on dissent in Xinjiang, which has been plagued by a series of attacks in public places. Xinjiang is the traditional home of the Uighur ethnic minority group.
Li said he had repeatedly called public security authorities, and he had not been able to communicate with Tohti.
"I simply don't dare to believe it, there's no way to confirm it," Li wrote on a social media app earlier. "If it really can be like this, I have no idea what route the legal process can take."
Tohti was known for championing the rights of the mostly Muslim Uighurs. Rights groups say the outspoken academic from the university in Beijing is being unfairly punished.
The PEN American Center said in a statement it was "deeply troubled" by reports that he may have been tried in secret. The organisation awarded Tohti a human rights prize in April.
China executed 13 people for "terrorist attacks" in different parts of Xinjiang on Monday and sentenced another three to death for a lethal attack at Beijing's Tiananmen Square.
Footage aired on state broadcaster China Central Television on Tuesday showed the 13 defendents standing on an outdoor platform, where they were sentenced before hundreds of people who appeared to be mainly Uighur.
Exiled Uighur groups and rights activists say the government's own repressive policies in Xinjiang have stoked unrest - a claim Beijing strongly denies.
A suicide bombing last month killed 39 people at a market in Urumqi, and 29 people were stabbed to death in March at a train station in the southwestern city of Kunming. (Reporting by Megha Rajagopalan, additional reporting by Ben Blanchard; Editing by Jeremy Laurence)