Madagascar's security forces on Thursday warned protesters to avoid attending any political demonstrations in the capital this weekend, citing a plot to incite a "blood bath."

"Those who still want to attend public demonstrations on Saturday should watch out," Florens Rakotomahanina, gendarmerie commander in Antananarivo province, told AFP.

He said the gendarmerie had received "reliable information to help foil an attempt to create a blood bath" aimed at destabilising President Andry Rajoelina, who seized power in a 2009 coup.

"The objective of this blood bath is probably to overthrow the current government," he said.

Rakotomahanina's comments were dismissed as scaremongering by the organisers of one planned rally, who are calling for an end to the post-coup crisis, that has seen politics and the economy paralysed.

"The police just want to scare people so they do not come to our event this Saturday," said Rainidina Rajoharison, a spokesperson for the Council of Christian Churches of Madagascar.

The group has called for national reconciliation and a change in the country's leadership.

Madagascar has been plunged deeper into crisis ahead of a presidential election that has repeatedly been put on hold amid controversy over the candidacy of the three front runners.

Regional mediators have called for Rajoelina, who seized power from Marc Ravalomanana, as well as Ravalomanana's wife Lalao and veteran leader Didier Ratsiraka, to step back from the polls.

But all three candidates have refused.

A presidential candidate also denounced Thursday's warning.

"If the police have tangible proof they should stop the mastermind behind this blood bath and haul them before court," said Alain Tehindrazanarivo.

"The law enforcement agencies are terrorising the population with their current behaviour," he said. "Shop owners are going to close their stores this Saturday while ordinary people will cloister themselves at home."

On Tuesday, police fired tear gas to break up an unauthorised election rally and arrested another presidential hopeful Laza Razafiarison.

The authorities said no permission had been asked to hold a public demonstration on Saturday.