Lowering the threshhold for the use of nuclear weapons, Russia has said it reserves the right to hit back with nukes in case of an aggression. This was disclosed in a new doctrine signed by President Dmitry Medvedev in Moscow. Some foreign diplomats believe that the lowering of threshold for the nuclear weapons could be a veiled warning to China, which has an overwhelming numerical advantage over Russia with the total population less than 147 million. Expansion of NATO closer to the boundaries of Russia, deployment of missile shield elements on the perimeter of its land and maritime borders, international terrorism, proliferation of WMD and growing number of nuclear powers have also been identified as the external threats for the security of the nation.