U.S. President Barack Obama has paid tribute to a Cuban dissident who died Friday.

Laura Pollan founded the 'Ladies in White' group after 75 dissidents, including her husband Hector Maseda, were imprisoned in a March 2003 government crackdown known as Havana's Black Spring. Dressed in white and each carrying a single white flower, the women defied government pressure by staging silent marches every Sunday on one of Havana's main avenues, demanding the release of their loved ones.

The White House said Pollan and her group “draw attention to the plight of those who are unjustly held in Cuba's prisons.”

U.S. diplomats, family members, government opponents and foreign dignitaries gathered at Pollan's house Saturday to remember the former teacher who died of respiratory failure in a Havana hospital.

The U.S. State Department called Pollan a “courageous human-rights defender” and said Cuba has “lost one of its most important voices of conscience.”

In 2005, the European Union honored Pollan's group with its human-rights award, the Sakharov Prize for Freedom of Thought.

By 2010, all the dissidents from 2003 were released, but the Ladies in White continued marching to protest Cuba's government.