Kidnapped aid workers released in Yemen, 5 militants dead SANAA/ADEN (Reuters) - Six kidnapped foreign aid workers have been released in Yemen, the defense ministry said Thursday, and a military source said separately that five Islamist militants were killed in clashes with the armed forces in the country's south. "The six aid workers were released...after mediation efforts led by Energy Minister Saleh Samee," the defense ministry said in a statement. They are in good health. It said the aid workers were of Yemeni, German, Palestinian, Iraqi, and Colombian origin. A U.N. source said the six worked for its Office for the Coordination of Humanitarian Affairs. Kidnappings, which come against the backdrop of relentless anti-government protests, have become common in Yemen where hostages are often used by disgruntled tribesmen to press their demands on authorities, and are usually freed unharmed. One of the kidnappers told Reuters the release was under way after a delay earlier when one of the hostages had fallen ill. He said the hostage was now well after receiving medical treatment, adding the government had agreed to release a tribesman in exchange for the hostages. The United States and neighboring Saudi Arabia are worried that political unrest could give al Qaeda's Yemen wing the opportunity to gain more control of the impoverished country. Protests have continued even after President Ali Abdullah Saleh transferred his powers and bowed to a year of mass protests demanding the end of his 33-year rule. Activists demand that Saleh, in the United States for medical care, be tried for alleged killings of protesters, and the government be purged of his relatives. In Yemen's south, four Islamist militants were killed and five more wounded in an army attack on two cars late on Wednesday in the city of Zinjibar, a military source said. Another car escaped unharmed. A fifth militant was killed by a sniper in the south of Zinjibar in a separate incident, said the source. The defense ministry said separately late Wednesday that a leading member of Yemen's security forces escaped an assassination attempt in the capital Sanaa. It said armed men fired at his car, wounding two of his bodyguards and wounding a young girl who was sent to hospital. Reporting by Mohammed Mukhashef and Nour Merza Additional reporting by Mohammed Ghobari in Sanaa; Writing by Nour Merza