The French Government has launched a controversial initiative to reform the country's pensions system.

Centre-right Prime Minister Jean-Pierre Raffarin said reform was overdue - but added that it would be gradual.

It will not be a question of brutally changing the rules of the game overnight Jean-Pierre Raffarin

He set 2020 as the target date for completing the first stages of the reform.

The speech to the advisory Economic and Social Council follows big demonstrations staged at the weekend in support of France's "pay-as-you-go" system - under which contributions from employees pay for current pensions.

Analysts say France's generous system is unsustainable - as stagnating birth rates and rising life expectancy means that in the future fewer workers will have to pay for increasing numbers of pensioners.

The prime minister made clear reforms would not be introduced suddenly.

"It will not be a question of brutally changing the rules of the game overnight," Mr Raffarin said.

"Those who are already retired will not be affected by the reform."

Contentious issue

Mr Raffarin also said he wanted to harmonise the public and private pension systems.

French public sector workers can retire on full pension after 37.5 years of contributions, while private sector employees must contribute for 40 years.

French leaders remember Juppe came unstuck over pensions

Mr Raffarin said the level and duration of contributions, as well as the amount of the pensions, would be the subjects of public debate.

He added that he would maintain the current right to retire at the age of 60.

A previous centre-right prime minister, Edouard Balladur, introduced some reforms of private sector pensions in 1993.

Two years later, a plan by his successor Alain Juppe to bring the public-sector regimes closer to private-sector provisions was withdrawn, following a wave of protests by public employees.

After this defeat, which contributed to Mr Juppe's fall from power, French Governments were reluctant to tackle the issue.

However when Mr Raffarin came to office last June, he vowed to makes pensions reform one of his priorities.

At the weekend at least 350,000 people took part in demonstrations in Paris called by trade unions to highlight their opposition to a radical change, such as possible moves towards private pensions.