Three French aid workers kidnapped in Yemen more than five months ago have been freed, the French presidential palace said Monday. "The president was informed tonight of the liberation of the three aid workers held in Yemen since May 28, 2011," it said in a statement. Tribal sources said in July that the three -- from French non-governmental group Triangle Generation Humanitaire -- were seized by Al-Qaeda militants in the Hadramawt town of Seyun, 600 kilometres (370 miles) east of Sanaa. Their car was found on the road some 20 kilometres from Shibam, a city known as the "Manhattan of the Desert" because of its spectacular high-rise mud-brick buildings, a Yemeni security official said at the time. On July 27, tribal sources said the "kidnappers are Al-Qaeda members and are demanding a ransom of $12 million" for the release of the three. The three appeared in an online video in September, saying their abductors' demands had not been met. Foreigners have frequently been kidnapped in Yemen by tribes who use the tactic to pressure the authorities into making concessions. More than 200 foreigners have been kidnapped in Yemen over the past 15 years, with almost all of them later freed unharmed.