The secret base, located in the southeastern Syria, at the border with Jordan, was used by U.S. and British special services as a transfer point for meeting rebels who enjoy support of the Western international coalition (Wall Street Journal). They never spent a single night there for security reasons. The 20 British special ops left the base about 24 hours before the attack.
The Russian military aircraft reportedly used cluster bombs during the air strike.
WSJ’s sources reported that the Russian military contacted Pentagon, saying that they attacked the base deliberately – they thought that the base was controlled by ISIS militants. However, a source in the U.S. intelligence said that it was absolutely clear that the base didn’t belong to the ISIS, as the outposts have unique constructive features that are not typical for militants.
After Pentagon warned the Russian air force that the base is being used by U.S. and British military, Russian aircraft delivered another attack on it – some 90 minutes after the warning. The U.S. pilots tried to contact Russians via special communication channel, but no response followed.