Russia has begun moving nuclear-capable missiles into Europe after America threatened to shoot down Russian planes over Syria, greatly raising the risk of all-out war.

Russian military appears to be moving nuclear-capable Iskander-M missiles from Saint Petersburg to Kaliningrad, a Russian enclave situated between NATO members Lithuania and Poland, according to sources inside Estonia.

The Iskander-M, which can fire a nuclear-armed missile over 300 miles away, is reportedly being transferred to Kaliningrad by ship approximately two years ahead of its previously scheduled deployment to the enclave.

In addition to its military deployments in Kaliningrad, Russia has deployed the S-300 and S-400 anti-aircraft missile systems to Syria after the Obama administration indicated covert air strikes on Syrian government forces are being considered to stop their advances in Aleppo.