Updated

Gabon President Omar Bongo, the world's longest-serving president whose 42-year rule was a throwback to an era when Africa was ruled by "Big Men," has died of cardiac arrest in a Spanish hospital. He was 73.

Doctors at the Quiron Clinic in Barcelona announced Bongo's death around 2:30 p.m. (1230 GMT, 8:30 a.m. EDT) Monday, Gabonese Prime Minister Jean Eyeghe Ndong said. Bongo was admitted to the hospital last month.

Only hours earlier, Ndong had said he saw the president and declared him "alive and well." Gabonese officials have become increasingly belligerent with journalists, including calling a meeting with the French ambassador in Gabon in order to discuss the coverage of the president's death by French media outlets.

Bongo, who was believed to be one of the world's wealthiest leaders, became the longest-ruling head of government — a category that does not include the monarchs of Britain and Thailand — when Cuba's Fidel Castro handed power to his brother last year.

The country's constitution calls for the head of the Senate, Rose Francine Rogombe, to assume power and organize presidential elections within 90 days of Bongo's death. But there has been speculation that one of Bongo's sons would try to seize power upon his father's death, as happened in nearby Togo.

Bongo had kept a tight grip on power in the oil-rich former French colony since he became president in 1967, and his ruling party has dominated the country's parliament for decades. Opposition parties were only allowed in 1990, amid a wave of pro-democracy protests.

Elections since then have been marred by allegations of rigging and unrest. In 2003, parliament — dominated by his supporters — removed presidential term limits from the constitution.

While most Gabonese genuinely feared Bongo and there was little opposition, many accepted his rule because he had kept his country remarkably peaceful and governed without the sustained brutality characteristic of many dictators.

Bongo, meanwhile, amassed a fortune that made him one of the world's richest men, according to Freedom House, a private Washington-based democracy watchdog organization, although nobody really knows how much he was worth.

Earlier this year, a French judge decided to investigate Bongo and two other African leaders on accusations of money laundering and other alleged crimes linked to their wealth in France.

The probe followed a complaint by Transparency International France, an association that tracks corruption. French media have reported that Bongo's family owns abundant real estate in France — at one time owning more properties in Paris than any other foreign leader.

Born Albert Bernard Bongo on Dec. 30, 1935, the youngest of 12 children, Bongo served as a lieutenant in the French Air Force, then climbed quickly through the civil service, eventually becoming vice president. He assumed the presidency Dec. 2, 1967, after the death of Leon M'Ba, the country's only other head of state since independence from France in 1960.

Bongo set up a one-party state. Six years later, he converted to Islam and took the name Omar.

His presidential security staff numbered 1,500, according to the U.S. State Department, while the entire military numbers just 10,000 troops.

Bongo sought international approval and in May 2004 he visited then-President Bush at the White House. He also tried to cast himself as a mediator, working to end conflicts in Chad and Central African Republic, where his country has a small contingent of peacekeepers.

Gabon is the fifth-biggest oil exporter in sub-Saharan Africa, and Bongo built a vast system of patronage, doling out largesse in part through the salaries and benefits that came with Cabinet posts.

But oil dependency means the country has more oil pipeline (886 miles) than paved roads (582 miles). Only 1 percent of its land is cultivated and Gabon produces virtually no food. Instead, basics such as tomatoes are imported from France, the former colonial master, and neighboring Cameroon, pushing prices so high that Libreville, the capital, is the world's eighth most expensive city, according to Employment Conditions Abroad International.

Ndong, the prime minister, went on state TV in Gabon late Sunday night to deny news reports in the French media that Bongo had died, saying: "I was surprised — like many of my compatriots — to learn from French TV that the President of Gabon is dead," he said.

"If such a thing were to happen, I believe and I know that the family of President Bongo would inform me. That is not the case for the moment. I have not been told of the death of the president of Gabon," he said.

Just hours later, he flew to Spain to hold a press conference at the Quiron Clinic, where he declared that the president was fine. Just before his death, he continued to insist that the head of state was only at the hospital for a checkup.