By Jan Lopatka and Jason Hovet

PRAGUE (Reuters) - Czech gymnast Vera Caslavska, her country's greatest Olympian and a powerful voice in its struggle against Soviet occupation, has died aged 74 of pancreatic cancer.

One of only two women to win back-to-back gold medals as best all-round gymnast, Caslavska took seven golds in all at the 1964 Olympics in Tokyo and the 1968 Games in Mexico City.

In the latter she competed against and beat Soviet athletes just weeks after Warsaw Pact tanks led by the Red Army swept into then Czechoslovakia to put down attempts to reform Communist rule.

"We went to Mexico determined to sweat blood to defeat the invaders' representatives," she told news website Aktualne.cz in a 2014 interview.

A lasting memory of those games is Caslavska's silent protest of bowing her head on the podium when the Soviet anthem played - echoing the more celebrated image of U.S. sprinter Tommie Smith's Black Power salute in solidarity with African American civil rights.

"Vera was a fighter. She was diagnosed last year in the spring," said Czech Olympic Committee President Jiri Kejval, who announced her death.

"When she did not come with us to (the) Rio (Games) it was clear the situation was bad," he told Reuters by telephone, adding Caslavska had died in her sleep.

Caslavska's other medals included back-to-back golds in the vault in the 1964 and 1968 games. She also won the beam in 1964 and the uneven bars and floor exercise in 1968.

Her main rival in Tokyo, Ukrainian-born Larisa Latynina, was the only other female gymnast to win successive golds in the all-round competition, in 1956 and 1960.

Competing for the Soviet Union Latynina, who finished second in 1964, recalled Caslavska with affection on Wednesday.

"She was a phenomenal sportswoman," Latynina told Reuters. "Vera and I were friends and we would give each other presents. We would also swap vinyl records."

TRAINING IN THE FOREST

Caslavska almost failed to make it to the 1968 Games after warnings she might face arrest sent her into hiding, forcing her to train in a forest for three weeks before state authorities allowed her to join the team in Mexico.

Following her triumph there, Caslavska was expelled from the Czech sports union and ostracized for criticizing the 1968 invasion and refusing to withdraw her signature from the Prague Spring protest movement's "Manifesto of 2000 Words" against Soviet interference.

From 1974 she trained other gymnasts at home and, between 1979-1981, also in Mexico.

When Communist rule ended in Czechoslovakia in 1989, new President Vaclav Havel made her his adviser for sport and social issues. She also led the Czech Olympic Committee from 1990 to 1996.

She was struck by personal tragedy in 1993 when her ex-husband, fellow Olympian Josef Odlozil, died from injuries suffered in a fall sustained after he was struck by their son Martin during a dispute. Martin Odlozil was convicted of causing his father's death but subsequently pardoned by Havel.

After a battle with depression, Caslavska returned to public life and was a member of the International Olympic Committee between 1995 and 2001.

During the 2014 Sochi Olympics, she rooted for the Ukrainian team in support of pro-European Union protests in Kiev, and criticized human rights abuses in Russia.

(additional reporting by Dmitriy Rogovitskiy in Moscow; editing by John Stonestreet)