Africa's longest-serving leader, Gabon's President Omar Bongo, has died in a Spanish hospital at age 73.

Gabon's prime minister, Jean Eyeghe Ndong, said Mr. Bongo died Monday after suffering a heart attack.  

Just hours earlier, the prime minister had denied reports of Mr. Bongo's death, declaring him "alive and well."

Shortly after announcing Mr. Bongo's death, Gabon's government declared it was closing the country's air, land and sea borders.

The Defense Ministry released a statement Monday saying that "all components" of Gabon's defense forces were being put in place.  The statement, which was read on television, also called for citizens to increase their "vigilance and patriotism" during this "difficult" time.

Gabon's Defense Ministry is headed by Mr. Bongo's son, Ali Ben Bongo Ondimba.

Meanwhile, Gabon's government has declared 30 days of mourning for the late leader, who led the West African nation for more than 41 years.

Gabon's constitution calls for the leader of the Senate, Rose Francine Rogombe to become caretaker president and organize a new election to replace the head of state.

In a statement Monday, President Nicolas Sarkozy of former colonial power France said his country remains by Gabon's side during this difficult time.

Mr. Sarkozy said France has lost a faithful friend who had the esteem and respect of his peers.

Mr. Bongo had entered a Barcelona hospital on May 21, about two weeks after suspending his duties as president.  

Officials at the time said he was trying to rest and recover after the recent death of his wife.  However, media reports said he had cancer.

Some information for this report was provided by AFP, AP and Reuters.