The ultimatum comes just days after the interim government said it was willing to talk to Zelaya provided that he pledge to respect results of elections set to be held in November.
Brazil 'will not comply'
Brazil's president, Luiz Inacio Lula da Silva, told reporters at a summit in Venezuela that Brazil would not agree to the demands by Roberto Micheletti, the interim Honduran president.
"Brazil will not comply with an ultimatum from a government of coup-mongers," Lula said, adding that international law protects Brazil's embassy.
Lula also demanded an apology from Micheletti.
Since last week, hundreds of soldiers and riot police have surrounded the embassy where protesters have held almost daily marches to demand Zelaya be reinstated.
The United Nations Security Council had condemned the purported harassment of the Brazilian embassy on Friday, after Brazilian officials complained it was "under siege".
Officials said food and supplies had only occasionally been allowed in and troops had blasted the building with high-frequency sounds.
Amid the ongoing political crisis in the central American country, the government issued a decree on Sunday allowing it to suspend freedom of speech, ban protests and suspend media groups because of "disturbances of the peace" since a June coup that toppled Zelaya, officials announced on Sunday.
Oscar Matute, the de facto interior minister, said media that "incite violence" should be regulated under the decree.
The clampdown was announced hours after four members of the OAS were expelled and five members detained for six hours at the international airport in the capital Tegucigalpa on Sunday.
|Police and security forces have launched major crackdowns on demonstrations [AFP]
The interim government had just last week invited the OAS to the country to help lay the groundwork for a mediation effort between the interim government and Zelaya.
But on Sunday, it rejected nine of 10 delegates.
John Biehl, the only OAS official allowed to enter Honduras, told the AFP news agency that one member of the group was sent to the United States and the three others were sent to Costa Rica.
"We were detained at the airport. There were two Americans, two Canadians, one Colombian and myself in the group," said Biehl, an adviser to Jose Miguel Insulza, the secretary general of the pan-American body, who is expected to visit Honduras later this week.
"We were detained for six hours ... as a Chilean, I have to say that it brought back some bad memories," Biehl said, alluding to the government under former leader Augusto Pinochet.
Two officials from the Spanish embassy were also turned back at the airport on Sunday as they returned to Honduras after vacationing abroad, a diplomatic source told the AFP.
The interim government took control of Honduras after the military, backed by the supreme court and congress, removed Zelaya from power in late June at the height of a dispute over his attempts to amend the constitution.
Critics say his push for constitutional amendments was to pave the way for a change in presidential term limits, in order to extend his rule, an accusation Zelaya denies.
Zelaya demands to be restored to power, but the interim government has said that elections in November will resolve the crisis.