Tensions rose in Honduras on Sunday in anticipation of fresh unrest after ousted leader Manuel Zelaya urged his supporters to stage a final offensive and coup leaders responded with a harsh warning to Brazil.

Raising the stakes further, meanwhile, five members of the Organization of American States were detained for six hours at the international airport in Honduras Sunday and four were expelled as they were attempting to enter the country, John Biehl, the only OAS official to enter the country, told AFP.

Farm workers from across Honduras were descending on the capital to voice support for Zelaya, religious leader Andres Tamayo told AFP from inside the Brazilian embassy in Tegucigalpa, where the deposed president has been holed up since he made a surprise return almost one week ago.

"A national call has been made for farmers and workers from other sectors to amass in Tegucigalpa, and some have already begun to form these much larger demonstrations," Tamayo said.

"Farmers are traveling by themselves, on public transport, because if they come in groups or in cars, the police and army will stop them at the checkpoints."

Zelaya has called on his supporters to converge on the capital on Monday, exactly three months after the coup, for a "final offensive against the de facto government."

"We're making a patriotic... call to resistance across all national territory," he said late Saturday in a statement handed to an AFP photographer inside the embassy.

Shortly after Zelaya's call for marches, the regime gave Brazil up to 10 days to define Zelaya's status in a statement read on national television.

It urged "that Mr Zelaya immediately stop using the protection that Brazil's diplomatic mission gives him to instigate violence in Honduras," warning it would otherwise take "supplementary measures," without elaborating.

Brazilian President Luiz Inacio Lula da Silva, thrown into the heart of the crisis, rejected any "ultimatum to the insurgents."

"The Brazilian government does not obey the ultimatum of the coup leaders nor recognize the interim government that seized power," he told reporters after participating in an Africa-South America summit in Venezuela.

Leaders of the resistance movement against the coup were meeting Sunday to work on a new strategy, amid high tension.

The interim government -- which took over after Zelaya was ousted in late June at the height of a dispute over his plans to change the constitution -- promised not to attack the embassy's "integrity."

Any attack on the embassy, Lula shot back, would be considered a "violation that contradicts all norms."

Coup leaders are seeking to arrest Zelaya for violating the constitution.

Tamayo, who leads the national resistance front, denied local media reports that Zelaya was seeking to install a "parallel" government, calling them "a lie."

Rather, the charismatic ousted president was awaiting the arrival of Organization of American States (OAS) chief Jose Miguel Insulza and other Latin American ministers to resume talks, said Rasel Tome, another resistance leader also staying at the Brazilian embassy.

It was not immediately clear how the drama surrounding the detention and expulsion of OAS members on Sunday would affect the talks.

The UN Security Council on Friday warned the regime headed by Roberto Micheletti not to harass the embassy, as Brazilian officials complained it was "under siege."

Demonstrators have come daily to the embassy compound, which is surrounded by anti-riot police and soldiers, to show their support for the embattled head of state.

Several thousand Zelaya supporters took to the streets again Saturday, in a march on foot and in scores of cars, waving red flags, honking horns and calling for him to return to office.

Zelaya said the regime had not responded to a call for dialogue, which he made after returning to the country, but had replied "with more repression against the people."

Two people have been killed in pro-Zelaya protests since the start of the week according to police, and rights groups have voiced concern about clampdowns on demonstrators and local media.

As hopes for dialogue dimmed, European Union countries said they would send back their envoys who were withdrawn after the coup, stressing that did not mean they recognized the interim regime.

With options for a rapid solution fading away, the United Nations on Wednesday also froze its technical support for a presidential vote scheduled for November.