The latest developments about Syria (all times local).

4:25 p.m.

Russia's foreign ministry says Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry have agreed to meet in Vienna with their counterparts from Saudi Arabia and Turkey to discuss the Syria crisis.

The statement released on Wednesday comes after Syrian President Bashar Assad went on a surprise visit to Moscow and met President Vladimir Putin.

Russia began carrying out airstrikes on Islamic State militants in Syria last month to support Assad's troops.