The foreign ministers of Russia, Saudi Arabia, the United States and Turkey plan to meet on Thursday in Vienna to discuss ways to resolve the Syrian crisis, a Russian Foreign Ministry source was quoted as saying by Interfax news agency.The source said that the meeting will be expanded to Friday, Interfax reported. "On Friday, the number of negotiators could be widened," the source added.Russia began air operations in Syria on Sept. 30 after receiving parliamentary approval. The Kremlin claimed the airstrikes, which followed a military build-up in Syria, aimed to support the forces of Bashar Assad, a long-standing Russian ally, against ISIS. However, Turkey and the West have accused Russia of targeting moderate fighters opposed to Assad, many of which are supported by Turkey and the U.S. Russia launched airstrikes against the opposition groups in Syria.