Bulgaria is pressing for the return from Libya of six medics convicted of infecting Libyan children with HIV.
The medics' imprisonment has been criticised by Western nations
Bulgaria's Foreign Ministry said it would send an official transfer request to Tripoli on Thursday.
Death sentences imposed on the six - five nurses and a Palestinian doctor who holds Bulgarian citizenship - were commuted to life in prison on Tuesday.
Libya's foreign minister said Tripoli was still awaiting guarantees regarding the treatment of the infected children.
"The ball is in the court of Bulgaria and the European Union," said Abdel-Rahman Shalqam.
Libya's High Judicial Council, a semi-political body, made the decision that the six should receive life sentences instead of the death penalty.
The move came after a compensation deal was agreed by the parents of the 483 infected children, reportedly worth $1m (£500,000) per child.
The payout is reportedly coming from an international fund which the Libyan government, the EU and other organisations are contributing to.
A further obstacle was cleared on Wednesday when another Libyan court cleared the six of defamation, a charge brought by a senior police officer after they claimed their initial confessions had been extracted under torture.
The six have been in prison since 1999 and were convicted in 2004 but say they are innocent. Bulgaria has lobbied internationally for their return.
"For us the case will be closed only after the medics return to Bulgarian soil, and we are working for it to happen as soon as possible," Bulgarian Prime Minister Sergei Stanishev told reporters on Wednesday.
Prosecutor General Boris Velchev said the request to Tripoli was based on a 1984 agreement that would allow the medical workers to serve their sentences in Bulgaria.
French President Nicolas Sarkozy may travel to Libya to mediate in the dispute between the two countries. A spokesman for Mr Sarkozy said Libyan leader Muammar Gaddafi had invited the president to Tripoli.
The medics were convicted of deliberately injecting 438 children with HIV-tainted blood. Fifty-six of them have since died.
TRIAL IN DATES
1999: 19 Bulgarian medics and a Palestinian doctor are arrested at a Benghazi hospital after an outbreak of HIV/Aids among children. 13 are later freed
May 2004: Libya convicts and sentences five Bulgarian nurses and the Palestinian doctor for infecting children with HIV. A Bulgarian doctor is freed
Dec 2005: Libyan Supreme Court overturns the convictions and orders a retrial
Dec 2006: Medics sentenced to death a second time
Feb 2007: Medics appeal to the Libyan Supreme Court
June 2007: Top EU officials hold talks in Libya to try to secure medics' release
11 July 2007: Libya's Supreme Court upholds death sentences
Foreign experts say the infections started before the medics arrived at the hospital, and are more likely to have been a result of poor hygiene.
Bulgaria, its allies in the EU, and the United States say Libya has used the case to deflect criticism from its run-down health service.
They have also suggested that not freeing the medics could carry a diplomatic price for Col Gaddafi, who has been seeking to emerge from more than three decades of diplomatic isolation.
The Palestinian doctor was granted Bulgarian citizenship to allow him to benefit from any transfer deal.