Al-Baghdadi al-Mahmudi, the last premier of deposed Libyan leader Moamer Kadhafi, is in critical condition after being tortured in a Libyan prison, his Tunisian lawyer charged on Wednesday.
Mahmudi "is in critical condition as a result of the torture he has suffered," said Mabrouk Kourchid, warning that "he could die".
The lawyer gave no further details nor did he reveal his sources for fear they could suffer reprisals.
But a Libyan official denied the torture charge and insisted Mahmudi was "in good health".
"Baghdadi al-Mahmudi has not been subjected to any ill-treatment and has been granted his full rights guaranteed by international law and the principles of human rights," Deputy Defence Minister Khaled al-Sherif said in Tripoli.
"The remarks of the lawyer are part of the political tensions in Tunisia," said Sherif, who is also commander of the national guard which runs a Tripoli prison where Mahmudi is being held.
The former prime minister fled to neighbouring Tunisia in September 2011, shortly after rebels seized Tripoli and effectively put an end to more than four decades of Kadhafi's iron-fisted rule.
He was arrested there and extradited to Libya last June, despite warnings from rights groups that he could face the death penalty and opposition from Tunisian President Moncef Marzouki.
He went on trial in November for what the prosecutor general's spokesman said were "prejudicial acts against the security of the state and financial crimes."
In July, Mahmudi protested his innocence to journalists visiting his prison.
"I am not guilty, not guilty, not guilty," he told reporters during a visit organised by the authorities in an apparent bid to quash rumours he had been tortured.
A physician by training, Mahmudi was loyal to Kadhafi until the end, serving as premier from 2006 up to the final days of his regime.
Along with Seif al-Islam, the toppled dictator's most high-profile son who is also on trial, Mahmudi is one of the few remaining keepers of the many state secrets under Kadhafi, who was captured and killed by rebels in October 2011.