Cuban police released dissident leader Mr Martha Beatriz Roque and two other women on Saturday but continued holding other opponents of President Fidel Castro detained in a roundup, a human rights group said.
Ms Roque, a 59-year-old economist who has been jailed twice since 1997 for criticising communist rule in Cuba, was freed without charge, said veteran activist Mr Elizardo Sanchez of the Cuban Commission for Human Rights.
Ms Roque and her driver were seized on Friday morning as police rounded up members of her opposition movement prior to a demonstration they had called outside the French Embassy in Havana to demand the release of political prisoners in Cuba.
"They were detained arbitrarily, with no warrants, without charges and not allowed to make telephone calls to their families who did not know where they were," Mr Sanchez said.
He said that at least 22 people were detained and that most were still being held including Ms Roque's top two political associates, lawyer Mr Rene Gomez Manzano and engineer Mr Felix Bonne.
Ms Roque, a diabetic, was resting at her Havana home, according to Mr Sanchez.
Ms Roque leads the Assembly for the Promotion of Civil Society, an umbrella group that organized an unprecedented opposition gathering on May 20 in the backyard of Mr Bonne's home to press for democratic change.
The latest detentions were apparently aimed at thwarting the protest Ms Roque had planned for Friday outside the French Embassy to encourage France and other EU governments to keep pressure on Havana to release dissidents jailed in 2003.