Mr Gao's family say they believe he is still alive
China has refused to comment on the case of a dissident lawyer who went missing one year ago.
Human rights groups, foreign officials and relatives of Gao Zhisheng have repeatedly urged Beijing to say where he is and what condition he is in.
But China has only ever given vague responses to requests for information.
Mr Gao's wife, now living in the US, said she was "certain" he was being tortured in prison and called on the US to increase its pressure on China.
At a regular news conference on Thursday, foreign ministry spokesman Ma Zhaoxu refused to answer questions from journalists about Mr Gao.
"I have made our position known many times, at least three times," the AFP news agency quoted him as saying.
"China is a country of rule of law and everything is handled according to the law," he said.
But Mr Ma said he might "refer to competent authorities for more specifics", said AFP.
US-based group China Aid said it believes Mr Gao is alive but suffering "extreme emotional and physical pain" in detention.
Mr Gao was taken from his house in Shaanxi province by police last year and has not been seen since.
Writing in the Washington Post, Geng He said she feared the authorities had taken her husband in retaliation for her leaving the country last year.
"We knew that if Zhisheng had tried to leave with us, we would never have made it out of China," she said.
"Now I wait, helpless, certain that my husband is being tortured and wondering whether I should actually hope that he has already been killed."
On Wednesday, a US embassy spokeswoman said Washington was "deeply concerned" about Mr Gao's safety.
"We have raised our concerns about Mr Gao's well-being and whereabouts repeatedly, both in Washington and in Beijing," said Susan Stevenson.
But Mrs Geng said US must increase its pressure and "cannot allow China to continue to act with impunity".
"China's lawyers are the country's only hope for becoming a one-party state where the rule of law prevails, let alone a true democracy," she said.
"If China continues to imprison its lawyers, there will be never be change."
Mr Gao was once named one of China's top lawyers by the country's Ministry of Justice.
But he angered the authorities with his campaigns on behalf of people who had lost land, injured miners and the banned spiritual movement, Falun Gong, among others.