The letter was billed by the newspaper as Sarkozy's first political intervention since he lost the 2012 election to Socialist Francois Hollande.
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It came after his lawyer said earlier on Thursday he would make a legal complaint against the phone-tappings, which were conducted in connection with investigations into the funding of Sarkozy's succesful 2007 election campaign.
Le Monde newspaper broke the news of their existence earlier this month.
"Today still, anyone who telephones me must know they are being listened to," he wrote. "This is not an extract from that marvellous (2006) film 'The Life of Others' on East Germany and the activities of the Stasi ... This is about France."
Prime Minister Jean-Marc Ayrault said in a statement that Sarkozy had made a "grave moral error" by attacking the judiciary and the police.
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Last week, a French court ordered a news website to withdraw a set of recordings secretly made by an adviser to Sarkozy during his 2012 election campaign.
Revelations in early March that the adviser, Patrick Buisson, had recorded hours of talks with the conservative leader and his entourage have caused uproar in the opposition UMP party ahead of local elections this weekend.
The separate phone-tapping revelations thickened the plot for Sarkozy, but have also caused problems for the Socialist government.
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Last week justice minister Christiane Taubira faced calls for her resignation after it emerged she had known Sarkozy's phone was being tapped - apparently contradicting an earlier statement.
The investigation into Sarkozy was originally about allegations, denied by the ex-president, that late Libyan leader Muammar Gaddafi funded his 2007 election campaign.
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