Russian and the United States have been accusing each other of the escalation of violence in Syria.

A Russian foreign ministry spokeswoman said the US would be supporting terrorists if it refused to fulfill Moscow and Washington's agreement on Syria. The spokeswoman also warned that if US "invades" Syria, as she put it, the Middle East would end up with "horrible structural change".

A US State Department spokesman said that Russian cities and planes would be under threat if the extremist groups in Syria grew. The State Department said the Russian operations in Syria are pushing moderate rebel groups into extremist camps.