Greece on Tuesday reshuffled its military chiefs amid a political crisis that could see a government downfall following a controversial decision to put an EU debt rescue deal to a referendum.

A state security council under Prime Minister George Papandreou replaced the heads of the general staff, the army, navy and airforce, and discharged a dozen army and navy officers, the defence ministry said in a statement.

A defence ministry source told AFP that the reshuffle was previously scheduled and not linked to political developments.

New military chiefs are appointed in Greece every two or three years.

The last appointments had been made by the previous conservative government in 2009, with the exception of the navy chief who was named last year by the present socialist administration.

But opposition parties attacked the government over the move.

"You're finished, hands off the armed forces," said conservative New Democracy shadow defence minister Margaritis Tzimas.

"There is no government in the country, one by one its lawmakers are jumping ship," Tzimas said, calling the reshuffle "undemocratic".

The other parties also questioned the government's motives.

"This heightens the climate of uncertainty and concern among public opinion," said the Democratic Left party.

Papandreou's shock announcement for a referendum early next year and a confidence vote on Friday sparked calls for early elections and a defection, leaving the government with just 152 deputies in the 300-seat parliament.

The hard-fought deal agreed last Thursday after marathon talks in Brussels included an agreement to write off 100 billion euros ($137 billion) of debt owed by Greece.

With leaders of the world's 20 biggest economies getting ready for a summit in Cannes focused on the economic crisis, Papandreou's unexpected move triggered fears that the EU's rescue efforts could rapidly unravel.