China's response

Russian disarmament experts say that China would inevitably respond by building more missiles, in order to improve the chance of penetrating US defences.



China could build more mobile missiles

It has also been suggested that other countries, such as India and Pakistan, could follow China's lead.

By relying on smaller and slower rockets to intercept incoming missiles, Mr Putin's proposed system would leave the ABM treaty intact.

The underlying principle of this treaty is that both the US and Russia (originally the USSR) should remain vulnerable to each other's nuclear arsenal.



Mr Putin, proposing a joint missile defence system, in an NBC interview

If either state were to neutralise the threat from the other - by building a national ABM system - it would no longer have to worry about retaliation, and would be more likely to launch a first strike.