The five Bulgarian nurses and one Palestinian doctor were pardoned on arrival in Sofia by Bulgarian President Georgy Parvanov.

The six touched down shortly before 10:00 am (0700 GMT) aboard a French presidential plane together with French first lady Cecilia Sarkozy and EU External Relations Commissioner Benita Ferrero-Waldner.

The medics were met at the airport by tearful relatives who had supported them throughout their eight-year ordeal, during which they spent three years on death row awaiting execution.

Libya said it had ordered their release after it was satisfied the conditions it laid down for extradition had been met.

"The matter has been settled. We received guarantees for the normalisation of relations with European countries and for a partnership agreement with the European Union," a Libyan official told AFP on condition of anonymity.

In Brussels, European Commission chief Jose Manuel Barroso confirmed that a deal on improving ties had been struck in order to secure the medics' release.

"I told (Libyan leader Muammer Gaddafi) that if this matter were settled we would do our best to further normalise these relations," he said.

Ferrero-Waldner said the release had cleared the way for "new and enhanced" EU ties with Tripoli, but did not go into details.

The EU currently has no bilateral agreements with Tripoli since imposing sanctions on Libya following the 1988 Lockerbie bombing, and has not started negotiations for an accord since UN sanctions were lifted in 2003.

The six medics were arrested in 1999 and convicted in May 2004 of deliberately infecting 438 children with HIV-tainted blood at a hospital in the Mediterranean city of Benghazi. Fifty-six children have since died.

They were originally sentenced to death but that was commuted to life in prison last week after a multi-million dollar compensation deal was hammered out with victims' families.

According to the Gaddafi Foundation run by Gaddafi's son Seif al-Islam, which has been involved in mediating the crisis, the compensation amounts to about one million dollars per child.

Following the medics' release, French President Nicolas Sarkozy stressed that neither France nor the European Union had paid "the slightest financial compensation".

Sarkozy also confirmed at a press conference in Paris that he would head to Tripoli on Wednesday for a "political trip" aimed at helping Libya reintegrate with the international community.

Cecilia Sarkozy and Ferrero-Waldner had flown to Tripoli on Sunday to push for the medics' swift release.

At one point, negotiations appeared to have stalled with Libya setting further conditions, including the normalisation of relations with the EU, as well as EU funding for infrastructure projects such as a cross-border motorway from the eastern border with Tunisia to the western frontier with Egypt.