Former prime minister Idrissa Seck, an emerging political rival to President Abdoulaye Wade, has been charged with endangering national security and remanded in custody until his trial.
Seck, who served as Wade's prime minister from November 2002 until April 2004, was formally charged on Saturday after spending a week in police detention.
During that time, Seck was questioned about allegations of massive overspending on public works in the city of Thies, where he serves as mayor.
The government has not spelled out publicly how Seck is supposed to have endangered national security or whether the charges against him are connected to allegations that he squandered 46 billion CFA francs (US $84 million) on public works projects in Thies that were only budgeted at 25 billion CFA (US $45 million).
Supporters of the 46-year-old politician have accused Wade of simply bringing the charges in order to silence a political rival.
Seck, who has made clear his ambition to become president, was taken into police custody on 15 July. He was transferred to the main prison in Dakar at the weekend after formal charges were laid against him.
Seck has repeatedly denied any wrongdoing and his defence team told IRIN that the charges against him were politically motivated.
“No specific fact was brought against him and no proof was submitted against him,” said Boucounta Diallo, the coordinator of his team of Senegalese and French defence lawyers.
“Mr. Seck is completely innocent of everything he has been accused of,” he added.
Ousmane Seye, a government lawyer, said Seck had refused to answer any police questions about municipal spending on public works in Thies, Senegal's second largest city, which lies 70 km east of the capital Dakar.
Widely regarded as a rival and potential successor to 78-year-old Wade within the ruling Democratic Party of Senegal (PDS), Seck has never denied that he has presidential ambitions.
However, he has consistently said that he would not stand against Wade if the aging president chose to seek re-election in 2007.
As the number two figure in the PDS, Seck played a key role in securing Wade's election as president and in constructing political alliances with minority parties that gave Wade's supporters 89 of the 120 seats in parliament in the 2001 general election.
He was made chief of staff of the president's office immediately after Wade's election and occupied the post for two years until he was made prime minister.
But the two men fell out last year and Seck was sacked as a result.
Wade's present drive to prosecute his former ally for "endangering state security and national defence" may prove difficult, since the constitution accords Seck certain privileges as a former prime minister.
Parliament must first approve the government's move to bring charges against Seck by a 60 percent majority.
If the legislature gives its consent, Seck will then be brought before a special court to be judged by a committee of eight senior judges and eight members of parliament.
Senegal has until recently had a reputation for democracy and tolerance in West Africa, a region plagued by military coups and civil wars.
The country has enjoyed uninterrupted civilian rule since independence from France in 1960 and Wade peacefully ended four decades of rule by the Socialist Party when he came to power in the 2000 elections.
But five years into his seven-year presidential term, Wade is facing increasing criticism for his increasingly authoritarian style.
In May, Abdourahim Agne, the vocal leader of the small centre-left Reform Party (PR), was arrested and charged with threatening the state after he urged people to take to the streets to demand Wade's resignation.
Shortly aftwards dissent broke out within the PDS's own ranks when 12 members of parliament close to Seck briefly defected from the ruling coalition.
Following their walkout, Seck’s home was attacked and a pro-PDS student leader was knifed.
Such incidents of political violence are relatively rare in Senegal, but they have become more common in recent years.
Diallo, Seck's chief defence lawyer, pointed out that ironically the president was bringing charges against Seck under four articles of the legal code which he had earlier vowed to abolish.
This special "High Court of Justice" was last convened in 1962 to hear charges that Mamadou Dia, the then prime minister had been plotting a coup against Senegal's first president, Leopold Senghor. He was found guilty and sentenced to life imprisonment.
Sidiki Kaba, the chairman of the Paris-based International Federation of Human Rights (FIDH), who is another lawyer in the defence team has no doubt why Seck is in prison.
"He is a political prisoner and we are defending him," Kaba said of Seck.