Three French aid workers held hostage by Yemeni tribesmen since May 28 have been freed after neighbouring Oman negotiated their release, paying an unspecified sum to their captors on behalf of the French government, a Yemeni tribal source said.

A source close to French President Nicolas Sarkozy declined to comment on whether a ransom had been paid.

The three hostages, two women and a man, worked for French charity Triangle Generation Humanitaire and had been kidnapped at a restaurant in the southeastern province of Hadramout.

The tribal source said they were in good health and had been taken straight to the Omani capital Muscat.

Sarkozy, who announced the news early on Monday, said he shared the joy of the aid workers' families.

The president warmly thanks the Sultan of Oman and the Omani authorities for their crucial help, as well as all those who contributed to this happy resolution, said Sarkozy in a statement, without saying how their release had been secured.

A spokeswoman for Sarkozy declined to provide further details.

Oman was also instrumental in negotiating the release of three Americans who were convicted by Iran of spying after straying across the border with Iraq.

Months of anti-government protests in Yemen have weakened already loose government control over swathes of territory, including Hadramout, where al Qaeda has been active.

Christian Lombard, head of Triangle, said the freed hostages would be flown back to Paris by Wednesday at the latest.

Kidnappings of Western tourists or workers by tribes seeking ransom or concessions from the government have been frequent in Yemen, one of the poorest Arab countries. Most hostages have been freed unharmed.

France still has five nationals held hostage overseas, four in Niger and one in Somalia.

(Reporting by Mohammed Ghobari in Sanaa and Christian Plumb in Paris; Additional reporting by Gregory Schwartz and Vicky Buffery; Editing by Alistair Lyon)