The founder of Cuba's Ladies in White dissident group, Laura Pollan, died in a Havana hospital aged 63, fellow activists said, hailing her work and lamenting the loss to the opposition's cause.

Pollan -- whose group has been at the center of efforts to promote change in Cuba after more than five decades of one-party Communist rule -- had been rushed to hospital a week ago after suffering acute respiratory distress.

"She just died -- her husband Hector Maseda was with her," a dissident who asked not to be named told AFP by telephone from Calixto Garcia Hospital in Havana on Friday.

The Ladies in White -- the wives and mothers of political prisoners who have emerged as influential dissidents in their own right -- based their operations from Pollan's home.

The group was founded after the arrest and imprisonment of 75 Cuban dissidents in 2003, including Pollan's husband.

Veteran dissident Martha Beatriz Roque -- who was one of the dissidents jailed in 2003 -- said Pollan had "given her life for freedom in Cuba."

Elizardo Sanchez, who heads the banned but tolerated Cuban Commission for Human Rights and National Reconciliation, said Pollan's death represented an "irreparable loss" to the country.

"She played an undisputed leadership role on the whole issue of human rights, but there are other women who can follow in her footsteps and continue her work," Sanchez said.

Blonde with a pale complexion, the diminutive Pollan had spent her career as a high school Spanish and literature professor, with a quiet tone but famously fierce convictions.

The Cuban government accuses the Ladies in White of provoking disturbances to highlight an alleged increase in repression, though Havana freed about 130 political prisoners between July 2010 and March 2011 with church mediation.

The women -- winners of the European Parliament's 2005 Sakharov Prize -- have asked the local Roman Catholic Church to mediate with the Americas' only one-party Communist regime, which refuses to allow political opening.

Activists from the group march peacefully in Havana every Sunday in white clothing, a color they say is intended to symbolize peace, often carrying gladioli.

An estimated 50 political prisoners remain behind bars in this Caribbean country of 11 million.