Opposition politicians and campaign groups in Senegal on Tuesday accused the government of secrecy after the BBC reported that a brother of the president had benefited from lucrative dealings in the gas sector.
The BBC report on Sunday, which the brother has denied, delved into contracts deriving from the discovery of major oil and gas reserves off the coast of the poor West African state.
It said that in 2012, newly-elected president Macky Sall confirmed a decision taken by his predecessor Abdoulaye Wade, to award exploitation rights for two fields to the Timis Corporation, controlled by an Australian-Romanian businessman, Frank Timis.
The BBC, in a report broadcast on its Panorama and Africa Eye programmes, said that two years later Timis Corporation secretly paid a "bonus" of $250 000 to Agritrans, a company controlled by Sall's younger brother, Aliou Sall.
Aliou Sall was also employed by the Timis group after his brother became president, receiving a salary of $25,000 per month, the BBC said.
He stepped down in October 2016 after being accused of a conflict of interest by the opposition. He was appointed head of a state-run savings deposit bank, the CDC, in 2017.
Aliou Sall on Monday denied the report, saying he would file suit against the BBC in Dakar and London for "libel."
"Agritrans never received $250 000 from Timis. The BBC's allegations are completely false," he said.
"Frank Timis obtained authorisation (to exploit the two fields) on January 17, 2012, when Macky Sall was not president. People are criticising me for being the president's brother," he complained.
A campaign group, Y'en a Marre ("Had Enough") said the BBC investigation "has once more revealed the opacity and lack of transparency surrounding negotiations and deals in these affairs."
It called on Aliou Sall to resign "and place himself at the disposal of justice."
The BBC also said the British oil giant BP paid Timis Corporation $250 million in 2017 in buy its exploitation rights, together with promises to pay up to $10 billion in rights over the next 40 years.
"This is an utter scandal," opposition lawmaker Mamadou Lamine Diallo told the daily VoxPop.
"We are going to fight to recover control over our natural resources, our gas, our oil."
BP denied any flaws in the deal.
Its chief executive for Africa, Emma Delaney, told the state daily Le Soleil that "reasonable and appropriate checks" had been carried out, and these specifically included verification of ethical and anti-corruption issues.