BARCELONA (Reuters) - Gabon's President Omar Bongo, Africa's longest-serving leader, died on Monday of a heart attack in a Spanish clinic after more than four decades of tight control over the central African oil-producing nation.
His death leaves a power vacuum. Analysts say factions within the ruling Gabonese Democratic Party (PDG) will be jostling to work out who succeeds him, with his son, Defence Minister Ali Ben Bongo, seen as a leading candidate.
The 73-year-old leader died at around 2:30 pm (1230 GMT) in the Quiron clinic in Barcelona, according to a statement issued at the hospital by Gabonese Prime Minister Jean Eyeghe Ndong.
"Throughout his political career, President Bongo always cultivated unity and cohesion among the Gabonese people," Ndong said, announcing 30 days of national mourning.
"At this moment of grief, the government calls on you to remain united in solidarity, in contemplation and dignity."
French radio said the Gabonese defence minister had ordered the closure of the country's air, land and sea borders.
The government said it would respect the terms of the constitution, under which Senate President Rose Francine Rogombe, a Bongo ally in the ruling Gabonese Democratic Party (PDG), is expected to take over as interim leader.
She should then organise elections within 45 days.
Bongo carved out a strong relationship with former colonial power France, and French influence is likely to continue.
French energy firm Total is one of the biggest investors in the country while the French military has around 1,000 troops stationed in the capital Libreville.
"All the French are interested in is continuity. They want the same leverage as they had, so a known candidate from within the (ruling) clan would seem to be preferable," said Hannah Koep, West Africa analyst at risk consultancy Control Risks.
French President Nicolas Sarkozy paid tribute to a "faithful friend" who he said "won the esteem and respect of his peers".
"France, faithful to its long friendship, remains by the side of Gabon, by its institutions, and by its people at this testing time," Sarkozy said in a communique.
Although there have been some concerns about stability, analysts say that the ruling party is likely to tightly manage the transition at least initially and that Bongo's successes in easing ethnic tensions will reduce the risk of turmoil.
Long-term investors such as Total or Royal Dutch Shell are unlikely to be phased by anything other than a sustained period of instability, while investors in its $1 billion Eurobond will look for little more than a commitment from the new administration to promise to buy back the issue.
So dominant was Bongo's personality over four decades that the opposition has had little opportunity to build much popular support. The potential for trouble lies more in the risk of fractures within the ruling elite, analysts say.
"The main pillar of stability has been Bongo himself," said Nicholas Shaxson, associate fellow at think-tank Chatham House.
"Nobody in the political opposition has any real grassroots support; it's within the ruling PDG where the tensions may lie."
Ben Bongo could face opposition from his brother-in-law, Foreign Minister Paul Toungui, while African Union Chairman Jean Ping, a long-time Bongo ally, and Vice-President Didjob Divungi Di Ndinge have also been cited as possible successors.
Despite the government's pledge to respect the constitution, there are precedents in West Africa for trouble after the sudden death of a long-standing president.
"In the Republic of Guinea, the constitution lasted about 20 minutes after the death of the president. In Togo, it didn't take very long to establish that the president's son was the best person to take over," said Antony Goldman, head of London-based risk consultancy PM consulting.
"The test for Gabon now will be whether the institutions have the capacity to accommodate the departure of the man who so dominated the system for such a long period of time."