DUBAI/ BEIRUT  - Al-Qaeda chief Ayman al-Zawahiri has urged rebels to fight to establish an Islamic state in Syria, in an online audio message Sunday in which he also warned France against its military intervention in Mali.“Let your fight be with the aim of establishing sharia (law) as the ruling system,” he said in his first message posted on the Internet since last November. “Do all that you can so that your war yields an Islamic state,” said Zawahiri, adding that such a state would help to re-establish the “caliphate” system of rule. “The enemy has begun to reel and collapse,” he said, referring to forces loyal to Assad.Rebel groups such as the Al-Nusra Front, which has links to Al-Qaeda, have eschewed the main opposition National Coalition, making it clear their goal is the creation of an Islamic state to replace President Bashar al-Assad’s regime. Zawahiri’s message will not sit easily with Western powers, who have expressed fears of extremist Islamism playing a growing role in the Syrian conflict and are reluctant to arm the rebels on the ground.Assad’s regime has long dismissed the rebels as “terror” groups backed by Western powers and driven by Al-Qaeda-style ideologies.The United Nations says more than 70,000 people have been killed in Syria’s two-year conflict, which broke out after the army unleashed a brutal crackdown against dissent, turning the uprising into a bloody insurgency.The Syrian opposition said on Sunday that a siege of Syria’s central city of Homs entered its 300th day on Sunday, as troops loyal to President Bashar al-Assad wage a campaign to oust rebel groups holed up there. “Three hundred days have gone by since the start of the siege of the heroic city of Homs, capital and beating heart of the Syrian revolution,” the Syrian National Council, a key component of the main opposition National Coalition, said.Daily battles rage on the edges of the insurgent neighbourhoods, and on Sunday, the army pounded the districts of Khaldiyeh, Qarabis, Qussour and Juret al-Shiyah. “Three hundred days have gone by while the world has looked on... with all kinds of war crimes and crimes against humanity being committed in this city,” the SNC said in a statement.“Schools and hospitals have been destroyed, water and electricity have been cut off, as have communications and food supply... Civilians are deprived of medicine and treatment,” the opposition group added.The SNC, meanwhile, denounced “the policy of sectarian cleansing” practised by Assad’s ruling minority Alawite clan against the Sunni population in Homs. The majority of Syria’s rebels are Sunnis, as is the population, and sectarian hatred has increased as the violence has grown steadily worse.According to an official study published in a newspaper on Sunday, Syria suffered in 2012 an unprecedented decline in foreign trade, with exports falling by nearly 100 percent from a year earlier.The study, published in pro-regime daily Al-Watan, showed “the dramatic impact caused by the current crisis” on foreign trade. The value of Syria’s exports registered in the year 2012 dropped to a mere $185 million, a decline of 97.4 percent on the $7.21 billion registered in 2011. In 2010 exports were valued at $11.35 billion.The study attributed the massive fall-off to “the large-scale destruction of the country’s infrastructure and industrial supplies, causing many enterprises to stop functioning”. Imports also suffered an unprecedented sharp decline of 78.4 percent in 2012, dropping to a value of just $3.58 billion from $16.57 billion a year earlier.The study blamed “the important role” played by international sanctions for the decline in foreign trade, which had pumped up the trade deficit and weakened the national currency. Other factors cited by Al-Watan that contributed to the drop were the fact that international sanctions had been slapped on an array of government officials, making it impossible for many countries to do business with Syria.The European Union and the United States have imposed sanctions targeting government officials besides imposing an embargo on trade in arms, an oil exports embargo and a ban on banking transactions to punish the Syrian regime’s crackdown on a revolt that broke out in March 2011.The Arab League also imposed a round of sanctions on Damascus, which froze trade transactions with the regime and exports into Arab countries.These sanctions also banned Syrian officials from travelling in the region, and prohibited the country’s airliner from operating flights to and from member countries.Syria is meanwhile suffering a food and oil crisis, and the UN has regularly denounced difficulties in providing aid to the country’s population, particularly in areas most affected by violence.