''The police extended detention...no reason was given,'' Ding told Kyodo News by telephone.

He said the notification came Tuesday, adding the police could yet further extend his detention.

But Hong Kong-based human rights watchdog Information Center for Human Rights and Democracy said the latest extension indicates there is not enough evidence to prosecute Liu and he could be released without charge before Jan. 24.

Liu, a prominent pro-democracy writer and rights activist who helped draft 'Charter '08,' was taken away by authorities in December last year and formally arrested for ''inciting subversion of state power'' in June.

The Charter, drawn up under the inspiration of Charter 77 of the then Czechoslovakia, calls for an end to one-party rule and a reformed political system based on human rights and democracy.

Dozens of other cosignatories were harassed by police during the preparation and release of the Charter, but only Liu was formally arrested.

Ding said Liu's health is currently ''quite fine.''

==Kyodo