Urgent action is needed to minimise the risk of a nuclear war, more than 120 senior military, political and diplomatic figures from across the world have warned.

Ahead of the Vienna Conference on the Humanitarian Impact of Nuclear Weapons, which starts today, the experts wrote in a letter that the danger of such a conflict was “underestimated or insufficiently understood” by world leaders.

The signatories include people from across the political spectrum such as former Conservative Defence Secretary Lord King, a Labour counterpart Lord Browne, former Foreign Secretaries Margaret Beckett and David Owen, and former Liberal Democrat leader Sir Menzies Campbell. John McColl, former Nato Deputy Supreme Allied Commander Europe, Lord Richards, former Chief of the Defence Staff, and General James Cartwright, former Vice-Chairman of the US Joint Chiefs of Staff, also signed the letter.

In pictures: The Nuclear Security Summit 2014 Show all 17 1 /17 In pictures: The Nuclear Security Summit 2014 In pictures: The Nuclear Security Summit 2014 The waiters who got the job The male waiters prepare the plenary table during a break at the 2014 Nuclear Security Summit on March 25, 2014 in The Hague, Netherlands In pictures: The Nuclear Security Summit 2014 The official group shot The heads of the delegations pose for an official group photo at the 2014 Nuclear Security Summit on March 25, 2014 in The Hague, Netherlands In pictures: The Nuclear Security Summit 2014 Talk amongst yourselves US President Barack Obama waves next to Chinese President Xi Jinping as they pose for a family picture with other world leaders, ministers and heads of international organisations on the second day of the two-day Nuclear Security Summit in The Hague on March 25, 2014 In pictures: The Nuclear Security Summit 2014 Angela Merkel and Sauli Niinisto German Chancellor Angela Merkel and Finnish President Sauli Niinisto at an informal plenary at the 2014 Nuclear Security Summit In pictures: The Nuclear Security Summit 2014 The opening session The opening session of the 2014 Nuclear Security Summit on March 24, 2014 in The Hague, Netherlands. In pictures: The Nuclear Security Summit 2014 Barack Obama and Mark Rutte US President Barack Obama shakes hands with Dutch Prime Minister Mark Rutte following a press conference at the Gemeentemuseum in The Hague on March 25, 2014 at the end of the Nuclear Security Summit In pictures: The Nuclear Security Summit 2014 The empty chair German Chancellor Angela Merkel looks at the empty seat of the US president in The Hague on March 25, 2014 on the second day of the two-day Nuclear Security Summit In pictures: The Nuclear Security Summit 2014 Maite Nkoana-Mashabane and Mark Rutte South African Minister of International Relations and Cooperation Maite Nkoana-Mashabane greets Dutch Foreign Minister Mark Rutte at The World Forum in The Hague on March 24, 2014 on the first day of the two-day Nuclear Security Summit In pictures: The Nuclear Security Summit 2014 View on the opening A general view of the opening session of the 2014 Nuclear Security Summit on March 24, 2014 in The Hague, Netherlands In pictures: The Nuclear Security Summit 2014 Helle Thorning Schmidt Danish Prime Minister Helle Thorning Schmidt arrives for meetings on the second day of the 2014 Nuclear Security Summit on March 25, 2014 in The Hague, Netherlands. In pictures: The Nuclear Security Summit 2014 Park Geun-hye and Barack Obama US President Barack Obama speaks next to South Korean President Park Geun-hye during a trilateral meeting with the Japanese prime minister at the US ambassador's residence in The Hague on March 25, 2014 after they attended the Nuclear Security Summit In pictures: The Nuclear Security Summit 2014 Federica Mogherini and Mark Rutte Italian Foreign Minister Federica Mogherini speaks with Dutch Prime Minister Mark Rutte during a session on the second day of the Nuclear Security Summit in The Hague on March 25, 2014 In pictures: The Nuclear Security Summit 2014 Julie Bishop Australian Foreign Minister Julie Bishop leaves at the end of the Nuclear Security Summit in The Hague on March 25, 2014 In pictures: The Nuclear Security Summit 2014 Ban Ki-moon and Barack Obama President Barack Obama chats with U.N. Secretary General Ban Ki-moon following the group photo at the 2014 Nuclear Security Summit on March 25, 2014 in The Hague, Netherlands In pictures: The Nuclear Security Summit 2014 Erna Solberg and Helle Thorning-Schmidt Norway's Prime Minister Erna Solberg, left, and Denmark's Prime Minister Helle Thorning-Schmidt, were two of the seven female leaders present at the summit. In pictures: The Nuclear Security Summit 2014 The G7 The G7 countries took the opportunity to discuss the recent developments in Ukraine during the Nuclear Security Summit. From left to right: President of the European Council Herman van Rompuy, Canadian Prime Minister Stephen Harper, French President Francois Hollande, British Prime Minster David Cameron, U.S. President Barack Obama, German Chancellor Angela Merkel, Japanese Prime Minister Shinzo Abe, Italian Prime Minister Matteo Renzi and President of the European Commission Jose Manuel Barroso In pictures: The Nuclear Security Summit 2014 The royals and Dalia Grybauskaite Dutch King Willem-Alexander and Queen Maxima greet Lithuania President Dalia Grybauskaite (right), at the Royal Palace Huis ten Bosch in The Hague, Netherlands, 24 March 2014

“Tensions between nuclear-armed states and alliances in the Euro-Atlantic area and in both South and East Asia remain ripe with the potential for military miscalculation and escalation,” says the letter to Sebastian Kurz, Austria’s Minister for Foreign Affairs.

“In a vestige of the Cold War, too many nuclear weapons in the world remain ready to launch on short notice, greatly increasing the chances of an accident.

“This fact gives leaders faced with an imminent potential threat an insufficient amount of time to communicate with each other and act with prudence.”