He said that he is seeking the resignation of the coup leaders who forced him into exile, arguing that international opinion was on his side.
Backing up that claim of international support, the US said on Wednesday that it had suspended $16.5m in assistance programmes to the Honduran government.
"It is going to be a dialogue for the departure of the coup leaders, Zelaya said, referring to Thursday's talks.
"It should not last more than one day - however, that has not yet been agreed upon."
Zelaya and Robert Micheletti, the man sworn in as his replacement hours after he was forced from the country, agreed to the mediated talks after Zelaya met Hillary Clinton, the US secretary of state, in Washington, DC.
Zelaya said that he had two specific aims in mind for the talks in Costa Rica.
"What is going to be done is to fulfil the resolution of the Organisation of American States and the resolution of the United Nations, in which they ask first and foremost for the reinstatement of the president of the republic," he said.
"Number two is the complete non-recognition of the authorities by coup d'etat, and condemnation of the coup d'etat."
The ousted leader said that the interim government has no legitimacy, pointing to the fact that governments across the world have condemned the coup.
"The [interim] government is completely disconnected from all of humanity. All the countries - the Arab countries, the African countries, the Asian countries, the European countries, the countries of the Americas - have all closed their doors to this government," he said.
But while Zelaya has demanded that he be swiftly reinstated as president, the interim government has maintained a tough line against him.
"This isn't a situation that can be resolved in a blink of an eye," Carlos Lopez, designated by Micheletti's interim government as envoy to the United Nations, said in Tegucigalpa, the Honduran capital.
Lopez reiterated the interim government's assertion that the Zelaya would face charges if he returned to Honduras.
Speaking to Al Jazeera on Wednesday, Antonio Rivera Callejas, a senator in the Honduran congress and a minority leader of the opposition National Party of Honduras, maintained that "what happened in Honduras was not a military coup - it was constitutional".
|Zelaya has the weight of international support behind him in the run-up to the talks [EPA]
"The supreme court, the 15 judges, by a unanimous decision, [ruled] that Zelaya was violating the laws in our constitution. Then the congress acted.
"The president was taken out of our country for his own safety. If he had stayed here, blood would have been on the streets."
Callejas added that "if Zelaya wants to come back, he is welcome, but he will be judged by all citizens."
Gabriel Elizondo, Al Jazeera's correspondent in the Costa Rican capital San Jose, said Arias has a huge task to fulfil in mediating a solution to the crisis in Honduras.
"To say Arias has a tough job is an understatement. He is basically going to have to do what the OAS and the UN has been unable to do, and that is come up with some sort of resolution," he said.
He added that Zelaya has a lot going in his favour.
"I think the coup leaders thought that Zelaya would go away peacefully into the sunset, but he has not," he said.
US suspends aid
Meanwhile, after nearly two weeks of mostly muted response from the US, Washington said on Wednesday that it had suspended $16.5m in military assistance programmes as well as development assistance programmes to the Honduran government.
It added that $50m more in assistance "could be in jeopardy" this year alone.
It added, however, that "programmes that directly benefit the Honduran people are continuing", including "supporting the provision of food aid, HIV/Aids and other disease prevention, child survival, and disaster assistance, as well as election assistance to facilitate free and fair elections".
Zelaya was removed from power on June 28 as he was about to press ahead with a non-binding referendum on the constitution.
His domestic critics said the public vote was aimed at changing the constitution to enable him to run again for office at the end of his current four-year term.
Zelaya attempted to return to Tegucigalpa, the Honduran capital, on Sunday but soldiers and military vehicles blocked the runway and warned off his aircraft.
At least one person among the thousands of people waiting for the plane to land was killed by security forces - the first to die in clashes since the coup.