India has signed a deal with Russia to acquire the S-400 air defence missile system, despite the possibility such a move could trigger US sanctions.

Indian Prime Minister Narendra Modi and Russian President Vladimir Putin announced the $5bn (£3.8bn) deal in Delhi on Friday.

The S-400 is one of the most sophisticated surface-to-air defence systems in the world. It has a range of 400km (248 miles) and can shoot down up to 80 targets simultaneously, aiming two missiles at each one.

India’s neighbour China also has the same system – the two countries fought a war in 1962 and routinely see skirmishes on their border. So for India it was imperative to boost its defence capabilities – especially in view of a possible two-front conflict, with Pakistan and China.

Rajiv Nayan, defence expert at the Institute for Defence Studies and Analyses think-tank, believes India had to take “a calculated risk”.

Read more about the deal between India and Russia here.