Qatar's Emir Sheikh Tamim bin Hamad al-Thani has warned that the US-led fight against Islamic State militancy will not succeed as long as Syrian President Bashar Assad remains in power.US and Arab forces have bombed Islamic State targets in northern and eastern Syria this week, following US strikes on the al-Qaida splinter group in Iraq since early August."We have to counter terrorism, yes. But I believe that the main cause of all this is the regime in Syria, and this regime should be punished," Sheikh Tamim said in an interview with CNN broadcast on Thursday."...If we think that we're going to get through the terrorist movements and leave those regimes doing what they -- this regime especially, doing what he is doing -- then terrorist movements will come back again," he said, according to a transcript of the interview.Islamic State fighters have exploited the chaos of Syria's three-year-old civil war, which pits Assad and his allies against mainly Sunni Muslim rebels and Islamist militants, to carve out territory in the country's eastern provinces.Qatar, which has sent cash and arms to rebels fighting Assad, also supported the US strikes against Islamic State, contributing one plane on the first night of attacks on Tuesday.Other US allies Jordan, Bahrain, the United Arab Emirates and Saudi Arabia have joined in the strikes. All are ruled by Sunni Muslims and are opponents of Assad, a member of a Shi'ite-derived sect, and his main regional ally, Shi'ite Iran.The air raids follow growing alarm in Western and Arab capitals after Islamic State, a Sunni militant group, swept through a swath of Iraq in June, proclaimed a "caliphate" ruling over all Muslims, slaughtered prisoners and ordered Shi'ites and non-Muslims to convert or die.