Russian President Dmitry Medvedev has threatened to quit a new nuclear arms reduction pact with the US, if it continues to build a missile defence shield in Europe.

He says he is also prepared to aim its new long-range Iskander missiles, armed with warheads, capable of foiling the shield at American command targets. The move places the US in a precarious position who says the systems are there to thwart its enemy, Iran.

Al Jazeera's Robin Forestier-Walker reports from Moscow.