Honduras de facto leader Roberto Micheleti demanded that Brazil hand over deposed constitutional president Manuel Zelaya who is currently in the Brazilian embassy in Tegucigalpa following a dramatic secret return to the country.
From Washington the OAS called on all sides for responsibility and prudence to avoid acts of violence that could impede national reconciliation.
In a televised address Monday evening Micheletti said Brazil would be held responsible for any violence.
A call to the government of Brazil: respect the judicial order against Mr Zelaya and turn him into Honduran authorities, he said.
The eyes of the world are on Brazil and Honduras.
Brazil's Foreign Minister, Celso Amorim, warned that any threat to Mr Zelaya or the Brazilian embassy would be a grave breach of international law.
Mr Zelaya's return took officials by surprise, with Mr Micheletti at first denying the deposed leader was in the country.
As tension inside Honduras increased, US Secretary of State Hillary Clinton said Mr Zelaya's return must not lead to violence.
”It's imperative that dialogue begin... (that) there be a channel of communication between President Zelaya and the de facto regime in Honduras,” she said.
Mrs Clinton spoke in New York after talks with Costa Rican President Oscar Arias, who has brokered failed peace talks between the two Honduran parties.
In images broadcast on national television, a smiling Mr Zelaya wearing his trademark white cowboy hat appeared on the balcony of the Brazilian embassy waving to a crowd of supporters.
Shortly afterwards officials imposed the 15-hour curfew, starting at 1600 (2200 GMT) on Monday.
Mr Amorim said neither Brazil nor the OAS had played any part in Mr Zelaya's return.
The interim government has repeatedly threatened to arrest Mr Zelaya should he return, and charge him with corruption.
Mr Zelaya urged the armed forces not to use violence against demonstrators.
OAS chief Jose Miguel Insulza also called for calm, telling Honduran authorities they were responsible for the security of Mr Zelaya and the Brazilian embassy.
Mr. Insulza is expected Tuesday in Tegucigalpa.
The OAS Permanent council in an emergency meeting Monday demanded the de facto government of Honduras to guarantee the life and physical integrity of deposed president Manuel Zelaya.
The council also asked the Honduras de facto leaders to sign the 12 point San Jose Accord proposed by Costa Rican president Oscar Arias, acting a mediator, and proposing the return of President Zelaya.
Finally OAS demanded from all sectors of the Honduran society “to act with responsibility and prudence, avoiding actions that could generate violence or impede national reconciliation” that is so cherished by the Honduran people and the rest of the continent.