The Organization of American States has given Honduras a 72-hour deadline for reinstatement or warned it could face suspension from the regional group.
Mr Zelaya has delayed his planned return home on Thursday, until the deadline expires at the weekend.
Interim leaders said he would be arrested for treason on his return.
The army ousted Mr Zelaya on Sunday over his plans for constitutional reform, which his critics said were aimed at prolonging his presidency.
Roberto Micheletti, the Speaker of Congress who was sworn in as interim president, said of the OAS deadline: "We can't negotiate anything.
"We can't reach an agreement because there are orders to capture the ex-President Zelaya here for crimes he committed when he was an official."
He told the Associated Press: "He can no longer return to the presidency of the republic unless a president from another Latin American country comes and imposes him using guns."
The president's expulsion has been widely condemned by leaders ranging from US President Barack Obama to Mr Zelaya's regional allies, including Venezuelan President Hugo Chavez.
Mr Zelaya, in Panama for the presidential inauguration, said: "I'm going to respect those 72 hours that the OAS asked for."
The US has suspended military co-operation with Honduras and says it will decide next week whether to cut aid.
Mr Zelaya's decision to postpone his return was described as "wise" by a senior official from US President Barack Obama's administration, quoted by Reuters news agency.
The World Bank and Inter-American Development Bank have cut new loans and some European countries have recalled their ambassadors.
The head of the OAS, Jose Miguel Insulza, condemned what he described as "an old-fashioned coup" in Honduras, after an emergency meeting of the regional grouping on Tuesday.
"We need to show clearly that military coups will not be accepted," he said.
But thousands of people demonstrated in the capital, Tegucigalpa, against the return of the ousted leader, whose popularity has slumped in opinion polls to around 30% in recent months.