Russian forces are preparing a military operation to help Syrian dictator Bashar Assad reclaim the last major cities held by rebel forces and terrorists, according to Moscow’s top diplomat.

“Terrorists systematically stage provocations and attack the positions of the Syrian army and communities and also the Russian air base Hmeymim with multiple rocket systems and drones,” Russian Foreign Minister Sergey Lavrov told reporters Monday, per state-run media. “Neither the Syrian army nor Russia will leave such outrages without crushing retaliation.”