WASHINGTON - US-led coalition aircraft bombing Islamist militants in Syria were re-routed at least once in the last six days to avoid a close encounter with Russian planes, a Pentagon spokesman said on Wednesday.The United States and its allies have been waging a year-long air campaign against Islamic State in Syria and across the border in neighboring Iraq. Russia launched air strikes in Syria last month, and has largely focused on hitting other rebel groups opposed to Syrian President Bashar Assad."We've had an instance at least where there's been action taken to make sure we didn't have an unsafe separation of space," said Captain Jeff Davis, a Pentagon spokesman. "We have had to do re-routing of the course of an airplane."Davis said the re-routing had occurred since an Oct. 1 secure video conference between US and Russian military officials, which focused on ways to keep air crews safe as they conduct parallel military campaigns with competing objectives.He declined to provide further details, including whether the aircraft involved was manned or a drone, or how often the modification had happened or where, except that it had occurred at least once, and in Syrian air space.