SAN JUAN, Puerto Rico—Lolita Lebron, a Puerto Rican independence activist who spent 25 years in prison for participating in a gun attack on the U.S. Congress a half-century ago, died Sunday. She was 90.

Lebron died at a hospital in San Juan of complications from respiratory disease, said Francisco Torres, president of the Nationalist Party of Puerto Rico. She had been hospitalized repeatedly in recent months for her ailments.

Lebron was a leading figure in the small but passionate nationalist movement in this U.S. territory.

"Lolita was the mother of the independence movement. This is an insurmountable loss," said Maria de Lourdes Santiago, a member of the Caribbean island's Senate from the Puerto Rican Independence Party.

Lebron was born Nov. 19, 1919, in Lares, in southwestern Puerto Rico, and moved as a young adult to New York, part of a mass migration from the island to the United States during the 1940s. There she developed her nationalist views and became a follower of movement leader Pedro Albizu Campos.

In 1954, she and three other nationalists entered the U.S. Capitol with automatic pistols and opened fire from an upstairs spectators' gallery onto the crowded floor of the House, firing nearly 30 shots. They unfurled a Puerto Rican flag and Lebron shouted "Viva Puerto Rico libre!"

No one died in the attack but five U.S. representatives were wounded, including one congressman who was shot in the chest.

Lebron later said that she never intended to kill anyone and that all four nationalists expected to be killed in the assault. She and the others -- Rafael Cancel Miranda, Irving Flores and Andres Figueroa Cordero -- received lengthy prison sentences.

President Jimmy Carter granted them clemency in 1979 and they were released.

"We didn't do anything that we should regret," Lebron said upon her release. "Everyone has the right to defend their right to freedom that God gave them."

Back in Puerto Rico, Lebron continued to attend political rallies on the island, where the independence movement holds little sway with voters. The vast majority of people in Puerto Rico favor either becoming a U.S. state or maintaining the semiautonomous status they have now.

Lebron was arrested in 2001 at age 81 when she and five other people cut through a fence on the neighboring island of Vieques to protest the 1999 death of a civilian security guard killed by an errant bomb dropped during a U.S. Navy training exercise. The U.S. has since closed the Vieques bombing range. She was sentenced to 60 days in jail for trespassing.

In recent years, Lebron tempered her support for violent struggle.

"I think times have changed, and there is no need now to kill for freedom," she told El Mundo newspaper in 1998. "I would not take up arms nowadays, but I acknowledge that the people have a right to use any means available to free themselves."

(This version CORRECTS date of birth and age to 90 instead of 89)

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