Capt Camara says he will lead an interim administration for two years
Thousands of Guineans have gone on to the streets of the capital to welcome the leader of a coup that followed the death of the country's president.
The junior army officer who led the coup, Capt Moussa Dadis Camara, told journalists he was now "president of the republic", AFP news agency reports.
He has declared an overnight curfew throughout the country.
A regional delegation is due in Guinea on Thursday to encourage a return to constitutional rule.
The group, Ecowas, has condemned the coup, as has the African Union.
"Ecowas cannot accept military imposition on the people of Guinea," said Mohammed Ibn Chambers, one of the delegation's members.
Earlier, government leaders insisted they were still in power and called for help from the international community.
But BBC West Africa correspondent Will Ross says the coup leaders now appear to be in control and to enjoy considerable public support.
President Lansana Conte, 74, died on Monday night and renegade soldiers moved to seize power in the hours afterwards, taking control of state radio and television.
The funeral of Mr Conte is to take place on Friday in his home village.
The BBC's Alhassan Sillah in the capital, Conakry, said that shortly after Capt Camara was named as president of the new junta, a large convoy of soldiers, policemen and firemen took to the streets in a large motorcade.
He said tens of thousands of people had come out to cheer and applaud them, shouting: "Welcome to this change; welcome to this change!"
The convoy moved through the streets unopposed.
"I came to see if the terrain is favourable to us," Capt Camara was quoted as saying. "I see that it is."
In his first press conference, the army captain said there was a big movement of support for the coup, AFP reported.
"I am convinced, reassured that I am the president of the republic, the head of the (junta's) National Council for Democracy and Development (CNDD)," he said.
Earlier, the CNDD announced a curfew from 2000 to 0600.
The coup leaders also warned forces loyal to the government against using mercenaries to restore themselves to power.
Coup leader Capt Camara makes a television address
"I would like to inform the people of Guinea that there are generals who for unknown reasons are trying to recruit mercenaries - some of whom are already inside our borders - for the purpose of destabilising our attempts to establish peace and democracy," Capt Camara said.
His statement followed a call by the parliament speaker, Aboubacar Sompare, for the international community to intervene.
According to Guinea's constitution, Mr Sompare should be in charge of the government until elections are held in 60 days.
The country's prime minister, Ahmed Tidiane Souare, has insisted the government, protected by loyal troops, is still the legitimate authority.
He rejected the coup leaders' claims that mercenaries could be used.
"It's idiotic - no, it's not true at all," Mr Souare told the Associated Press news agency.
"We are still in control and we are trying to normalise the situation. We have no intention of bringing in mercenaries. In fact, we haven't even asked our own armed forces to intervene."
Capt Camara said the new ruling council replacing the government and other institutions would hold "free, credible and transparent elections" in December 2010, when President Conte's term would have ended.
"The council has no ambitions to hold on to power. The only reason is the need to safeguard territorial integrity. That is the only reason. There is no ulterior motive," he said.
Mr Conte died on Monday night after a "long illness".
The cause of his death is unknown, but Mr Conte was a chain-smoker and diabetic who is also believed to have suffered from leukaemia.
The European Union and United States have joined the African Union in condemning of the coup.
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