Rex Tillerson, the US secretary of state, warned Saudi Arabia and Iran yesterday not to use Lebanon as “a venue for proxy conflicts” amid fears that their power struggle would destabilise the small country and cause fresh chaos in the region. One week after after Saad Hariri, the Lebanese prime minister, abruptly resigned during a trip to Saudi Arabia questions continued to mount over whether he was being effectively held prisoner in Riyadh. The tensions over Mr Hariri’s fate and other issues prompted the United Nations secretary general to appeal for calm and warn that a fresh conflict in Lebanon would have “devastating consequences” for the Middle East. “The United States supports the stability of Lebanon and is opposed to any actions that could threaten that stability,” Mr Tillerson said in a statement. “The United States cautions against any party, within or outside Lebanon, using Lebanon as a venue for proxy conflicts or in any manner contributing to instability in that country.” Without naming specific countries or groups, he said all regional players must “respect the integrity and independence” of the Lebanese government and military and called Mr Hariri “a strong partner of the United States”. Emmanuel Macron spent two hours in Saudi Arabia meeting with Mohammed bin Salman, the kingdom's powerful crown prince His statement came amid concerns that Mr Hariri had been forced to resign by Saudi Arabia as part of its efforts to counter Iranian influence in Lebanon. It also contrasted with tweets from Donald Trump, who said he had “great confidence” in Saudi Arabia and the leadership of its aggressive young crown prince, Mohammed bin Salman. Mr Hariri has remained in Saudi Arabia since resigning on Saturday, and while he has met with Western diplomats he has not done any interviews nor made contact with some of his closest aides. Many Lebanese suspect he is under house arrest in and Lebanon’s president has said he will not accept his resignation until he returns to the country to deliver it in person. Even Mr Hariri’s own political party, the Future Movement, has indicated he is being held against his will. Emmanuel Macron, the French president, visited Riyadh briefly on Thursday and the French government gave mixed signals over whether it felt Mr Hariri was at liberty or not. Jean-Yves Le Drian, the French foreign minister, said he though the Lebanese politician was “free of his movements” but a spokesman later appeared to walk the comment back and called for him to be able to return to Lebanon. Posters in solidarity with Mr Hariri have gone up in parts of Lebanon Credit: REUTERS/Mohamed Azakir Both the US and Germany said they had seen no evidence that Mr Hariri was being held captive. The leader of Hizbollah, the Shia militant group which plays a major role in Lebanon’s politics, said Mr Hariri was a prisoner in Saudi Arabia and that his detention was an insult to all Lebanese. António Guterres, the UN secretary general, expressed fears that the tensions would lead to a fresh conflict in Lebanon, eleven years after fierce fighting between Israel and Hizbollah left thousands dead. "It is essential that no new conflict erupt in the region,” Mr Guterres said. "It would have devastating consequences." Most analysts expect that neither Hizbollah nor Israel are seeking war and that if Saudi Arabia does lash out against Lebanon it is likely to be in the form of economic sanctions, like those it imposed on Qatar.