Speculation over a formal separation has mounted in recent weeks, particularly after the president's spokesman refused to confirm or deny reports of an imminent break-up earlier this month.

Mr Sarkozy, 52, married his 49-year-old wife in 1996. The couple have a 10-year-old son, Louis, and two children each from previous marriages.

On Wednesday, the weekly news magazine Le Nouvel Observateur's website reported that the pair had appeared before a judge to seek a legal separation on Monday.

However, the LCI news channel said Ms Sarkozy had seen a judge alone, and that the judge had later visited the presidential Elysée palace to give Mr Sarkozy a document to countersign.

The Sarkozys' marriage has often been the subject of speculation in the French press, breaking media taboos on the reporting of politicians' private lives in France.

The couple separated briefly in 2005, when Ms Sarkozy had an affair with an advertising executive. Although they got back together in a blaze of publicity at the start of last year, she played no public part in her husband's election campaign.

She did not vote for him at the second-round ballot, and has accompanied him in an official capacity only three times - the last of them in July - since he won the presidency in May.

Rumours were rife when Ms Sarkozy failed to join her husband for lunch with the US president, George Bush, in the US in August.

The French leader and his wife were spending their holidays in the area, but she cancelled, claiming a severe sore throat. She was later seen shopping with friends.

Asked about her possible role as the president's wife two years ago, she said: "I don't see myself as a first lady. It bores me. I'm not politically correct."

Today's announcement came as Mr Sarkozy faced the challenges of a crippling two-day public transport strike in protest at his pension reform plans and an EU summit in Lisbon on the new reform treaty.