The conflict in Syria has more than halved the amount of oil the Middle Eastern country can supply, the Organization of the Petroleum Exporting Countries (OPEC) said on Tuesday.
The influential oil exporters' group also said that demand for oil had risen this year as the picture for the global economy improves. OPEC revised its demand forecasts up by 25,000 barrels a day in 2013.
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A subdued improvement in developed world economies, such as the U.S. and Europe, has offset a slowdown in emerging and developing economies, according to OPEC.
"Risks to the forecast remain high due to weather, natural decline, technical, political and environmental factors," the group warned.
Syria is expected to have one of the largest declines in oil supply this year, as conflict continues to rage in the country.
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OPEC expects Syria's oil supply to decline by 120,000 barrels a day to an average of 90,000 barrels a day in 2013 – although the country's troubles mean it is difficult to collect accurate data. This is small in the context of the demand for OPEC crude, forecast to average 29.9 million barrels a day in 2013.
The Syrian regime's alleged use of chemical weapons against its own people, which President Bashar Assad denied authorizing in an interview at the weekend, has led to a global standoff over whether other governments should take military action in the country. This caused the oil price to jump in August as concerns about trouble in the rest of the region spread.