Nicolas Sarkozy made a dramatic return to the French political scene on Friday, slamming a decision to deny his right-wing UMP party millions of euros in campaign reimbursements and issuing a call to arms to his supporters.
Sarkozy, defeated by Socialist Francois Hollande in last year's presidential vote, denounced the "unprecedented" decision to deny his party campaign funds and vowed to "take on my responsibilities".
With his party stuck in a divisive leadership battle and now facing financial chaos, the 58-year-old Sarkozy appeared to be positioning himself for a political comeback.
Party sources said Sarkozy would attend an extraordinary meeting of the UMP leadership on Monday.
An enraged Sarkozy on Thursday took the unexpected step of resigning from the Constitutional Council, France's top constitutional body, after it upheld a decision by election auditors to deny the UMP a reimbursement of about 11 million euros ($13 million) because it breached campaign spending limits.
In a statement on his Facebook page, Sarkozy said the council's decision "threatens the political party that must prepare the so-necessary alternative to Socialism".
"I have to take on my responsibilities by committing myself to guaranteeing the freedom of democratic expression in our country," Sarkozy said.
"I ask you to help me by mobilising, as I will, to this end," he said, urging supporters to make donations to the party.
The council, which former presidents join automatically, concluded that the UMP had breached the spending ceiling by 2.1 percent so was not eligible for the reimbursement of 47.5 percent of total campaign expenses it had been due.
-- 'Hard blow' to Sarkozy's party --
It was the first time a candidate reaching the second round of a French presidential election was not reimbursed for campaign expenses.
Right-wing newspaper Le Figaro said the decision dealt a "hard blow" to Sarkozy's party and "threatens to exacerbate the UMP's already very-difficult financial situation."
Popular daily Le Parisien said Sarkozy's resignation from the council marked the first step in his comeback attempt.
"War has been declared," the paper wrote, quoting Sarkozy aides saying they believed the council's decision was orchestrated by the government to damage Sarkozy and the UMP.
Speaking during a visit to Tunisia, Hollande called on all French politicians to "fully respect" constitutional council decisions.
"Nobody can spread suspicions (or) question this institution without questioning the institutions as a whole," the president said at a press conference in Tunis.
Justice Minister Christiane Taubira earlier expressed "surprise" at Sarkozy's criticism of the council, saying that by contesting its decision he was acting "in defiance" of state institutions.
She urged him to behave "with dignity in the name of the public interest".
The UMP has been struggling since Sarkozy's defeat, with party leader Jean-Francois Cope and ex-prime minister Francois Fillon embroiled in a bitter public leadership battle that has hurt its reputation.
Sarkozy remains the favourite choice of UMP supporters to be the party's candidate in the next presidential election in 2017, with 87 percent in a recent poll hoping he will run.
Sarkozy has stayed out of the political spotlight since his loss, resuming his corporate law practice and lecturing on the international circuit, but has suggested he could return out of a "duty" to the French people.
Hollande meanwhile has seen his popularity ratings plummet after unemployment hit record highs, the economy slid into recession and government spending cuts began to bite.
A recent poll put Hollande's confidence rating at only 27 percent.
Still, few expect a political return for Sarkozy to be easy. Outside of right-wing circles, Sarkozy was a deeply unpopular figure going into last year's election, criticised for his flashy style and abrasive personality.
He is also at the centre of a series of ongoing criminal investigations, including accusations his 2007 campaign accepted envelopes stuffed with cash from France's richest woman, Liliane Bettencourt, when she was too frail to know what she was doing.
Prosecutors have recommended that the charges against Sarkozy in the Bettencourt case be dropped, but a number of other probes are continuing, including into allegations that he accepted up to 50 million euros from former Libyan strongman Moamer Kadhafi for the 2007 campaign.