Brazilian architect Oscar Niemeyer, who designed much of the country's futuristic capital Brasilia, died Wednesday, his doctors said. He was 104.

A pioneer in the use of reinforced concrete to produce soaring, curvaceous forms, Niemeyer has designed 600 works around the world and has some 20 other projects under way.

The Brazilian icon, who won architecture's top award, the Pritzker Prize, in 1988, started his career in the 1930s and went on working well into the 21st century, after turning 100.

"I am not attracted by the angles or the hard and inflexible straight lines created by man," Niemeyer once told the Spanish newspaper ABC.

"What attracts me is the free and sensual curve, the curve which I find in the mountains of my country, in the flow of its rivers, in the waves of the ocean, in the body of a woman."

Niemeyer works can be found in countries as far-flung as Algeria, Italy, Israel, the United States and Cuba, whose longtime leader Fidel Castro was one of his personal friends.

In the 1940s, he worked on the headquarters in New York of the recently-created United Nations, an initiative which symbolized hopes for a new era of peace after the carnage of World War II.

On that and other early projects, Niemeyer teamed up with another pioneer of post-war buildings in concrete, the French-Swiss architect Charles-Edouard Jeanneret-Gris, better known by his pseudonym of Le Corbusier.

In 1956, Niemeyer was appointed chief architect on the project to provide Brazil with a modern new capital city in the heart of the Amazon basin jungle -- an achievement that was to make him one of the world's best-known architects.

One of his most spectacular works was a contemporary art museum created in 1996 -- when Niemeyer was already 89 years old. Located in Niteroi, a town near Rio, it includes an upturned dish shape poised over the ocean on rocky cliffs.

"Architecture is done by governments for the rich," Niemeyer, a lifetime communist, once said.

"Poor people don't get to take part, but they can be brought to a halt in front of a building which is so different that it sparks a moment of surprise and emotion."

Niemeyer created some 400 buildings in all, including the Serpentine Gallery in Hyde Park, London, the Penang State Mosque in Malaysia, and the headquarters of the French Communist Party in Paris.

The latter building was designed during a period of exile in France, where the architect fled in the 1960s when a military dictatorship seized power in Brazil.

"There are too many injustices. But commitment to the Communist Party provides hope, solidarity, and the realization that it is possible to struggle together for a better world," he told the French Communist daily l'Humanite in 2006.

Niemeyer was born on December 15, 1907 in Rio de Janeiro into a middle-class family of German, Portuguese and Arab ancestry. He studied at the city's Fine Arts Academy, becoming an engineer-architect in 1936. One of his first jobs was on the Brazilian pavilion at the World Fair of 1939 in New York.

In 1928, he married Annita Baldo, with whom he had one daughter. The marriage lasted 76 years until Annita's death in late 2004. His only daughter, Anna Maria Niemeyer, died of emphysema in 2009 at the age of 82.

Niemeyer had been hospitalized several times in recent years, including for a 2009 surgery on his gall bladder and to have a tumor removed from his colon.

The architect, who died just shy of what would have been his 105th birthday on December 15, was hospitalized on November 2 suffering from dehydration after coming down with the flu. It was the latest in a series of lengthening hospital stays.

He remained busy to the very end of his life.

Earlier this year, Niemeyer supervised the renovation of the iconic Sambadrome, the "temple of Samba" which he designed 30 years ago and where the raucous parades of Rio's Carnival are held each year.