The leaders of 47 countries have met in the United States capital Washington to discuss nuclear weapons and how best to contain the threat they pose.

China, India and Pakistan are among the countries attending the two-day summit. Prior to the meeting, President Barack Obama warned that terrorist organisations such as al-Qaeda would not hesitate to use a nuclear weapon against the United States.

Iran and North Korea have not been invited because they allegedly violate the nuclear non-proliferation treaty intended to limit the spread of nuclear weapons and promote disarmament and the peaceful use of nuclear technology. Syria was not invited because the US government believes it has nuclear ambitions.

Last week, the US and Russia signed a treaty radically which will drastically reduce their nuclear arsenals.