Russia is mobilizing for its biggest military exercise since the height of the Cold War, the Kremlin says, citing a tense international climate that is “frequently aggressive and unfriendly toward us.”

The exercises, which are set to involve nearly 300,000 Russian troops, 1,000 aircraft and 900 tanks, will also include units from China for the first time. They will start on Sept. 11.

In a separate display of military power, Russia was reported on Tuesday to have assembled a large flotilla of warships off the coast of Syria. Russian news media outlets, citing unnamed defense ministry officials, described it is as Russia’s largest naval deployment in the area since Moscow first intervened in Syria’s civil war in September 2015.

The move follows a flurry of claims by Russia, unsupported by evidence, that the West is preparing to stage a fake chemical weapons attack inside Syria as a pretext for an assault on the forces of the Syrian dictator Bashar al-Assad.