BEIRUT (Reuters) - Lebanese President Michel Aoun expressed concern on Friday over reports surrounding the circumstances of Saad Hariri, who resigned as Lebanese prime minister on Saturday while in Saudi Arabia. Aoun, in a meeting with foreign ambassadors and representatives of the United Nations, EU and Arab League in Lebanon, urged clarification of these circumstances, presidential sources said. Two top Lebanese government officials told Reuters on Thursday they believed Hariri was being held in Saudi Arabia. A third source, a senior politician close to Hariri, said Saudi Arabia had ordered him to resign and put him under house arrest. A fourth source familiar with the situation said Saudi Arabia was controlling and limiting his movement. Riyadh says Hariri is a free man. 