TEGUCIGALPA - The rivals in Honduras' political crisis open new talks on Tuesday to discuss the proposed return of ousted President Manuel Zelaya, a thorny issue that could derail the fragile negotiations altogether.

The standoff is Central America's worst crisis in years and has become a test for U.S. President Barack Obama after he promised better relations with Latin America.

Envoys for the leftist Zelaya, who was toppled in a June 28 military coup, and for the de facto government led by Roberto Micheletti made some headway on other issues in talks last week.

But Zelaya, who crept back into the country in late September and has been holed up in the Brazilian embassy since then, says Micheletti has no intention of allowing his return to power.

We are not optimistic about the result of the dialogue, Rasel Tome, a close aide to Zelaya with him in the embassy, told Reuters on Monday. Part of Zelaya's negotiating team may walk out of the talks if progress is not made.

Many countries, including the United States, have threatened not to recognize elections for a new president on November 29 if Micheletti does not first allow Zelaya's return. Obama has frozen some economic aid to the country.

Zelaya's supporters plan a series of protests this week. They are threatening to disrupt the election campaign and block voting centers if their leader is not reinstated in the next few days.

Micheletti's government is accused of human rights abuses by Amnesty International and has broken promises to quickly lift curbs on protests and on media loyal to Zelaya.

Some U.S. Republicans have criticized Obama for sticking up for Zelaya, a close ally of Venezuela's socialist President Hugo Chavez. They want the United States to recognize the November elections.

Jose Miguel Insulza, who heads the Organization of American States, said he was hopeful for more progress in the next few days.

Ideas are circulating about different time frames for the return of the president, he told CNN's Spanish language channel on Monday night.

(Reporting by Magdalena Morales and Luis Rojas; Editing by Kieran Murray)