BEIJING  Teng Biao is no stranger to the wrath of the Chinese authorities.

One of a handful of lawyers in China pressing for human rights and the rule of law, he has been repeatedly detained, beaten and threatened with death.

But this latest spell of detention  he has been held by Beijing security officers for three weeks, with no word from him or his captors  has struck a new chord of anxiety in his wife and friends.

“This time is really strange,” said his wife, Wang Ling. “In the past, they held him only a few days, and we knew for what reason. But this time, I’ve been told nothing. No news, no calls, no result so far. I have no idea at all.”

Mr. Teng is one of many prominent rights defenders and advocates who have disappeared and are being detained, some with no legal authority, in what critics say is one of the harshest crackdowns in many years. The detainees’ relatives and supporters say previous periods of confinement did not last this long and in such total silence. The crackdown is part of a broader push to enforce social stability that has grown more intense in the past three weeks.