Antananarivo - Forty-eight inmates broke out of the main prison in Madagascar's capital Antananarivo on Sunday and another 23 would-be escapees were captured, police said.

The breakout, which began as inmates set fire to part of the facility, ended a few hours later with several of the escapees caught just outside the gates and others rounded up at roadblocks, a police crisis unit official said.

Some of those caught were injured, he said, without elaborating.

Jacques Sylla, the "prime minister" of Madagascar's self-proclaimed president Marc Ravalomanana, said President Didier Ratsiraka was behind the incident.

"We have noticed growing pressure on the part of the Ratsiraka camp on the city of Antananarivo, first through shortages, certain problems in businesses, and today maybe this option," Sylla said at the prison.

A blockade imposed on the capital by supporters of Ratsiraka - locked in a dispute with Ravalomanana over the outcome of a presidential election in December - has resulted in fuel and food shortages in Antananarivo.

Sylla said: "One could assume that there was external help, even if one cannot be categorically sure."

He said he would step up security in the capital and neighboring towns.

"More patrols are beginning to circulate, roadblocks have been set up at the periphery but also in some other surrounding towns," he said.

The "police minister" in Ravalomanana's government supported Sylla's claim that the mutiny had outside help.

"It is very likely that there was external help, and it's not by chance that it happened today," said General Augustin Amady.

"Those prisoners have been there for a long time without ever having agitated, so why today?" he asked.

The fire burned down an outbuilding and damaged part of the main prison.

Sugar, salt, flour, oil and other basic foods have disappeared from the supermarket shelves in the capital, while the price of rice has shot up by 50 percent. - Sapa-AFP