Action to limit the risks of a deliberate or even accidental nuclear attack is “insufficient”, a pan-global group of political, military and diplomatic figures has warned.

Ready-to-launch nuclear weapons mean the risk of an accidental strike by a nation state is high, while insecure stockpiles could be targeted by terrorists, the European Leadership Network said.

In a letter ahead of the Vienna Conference on the Humanitarian Impact of Nuclear Weapons, British signatories including former defence secretaries Lord Browne and Lord King, former home secretary Charles Clarke and Lord Richards, former chief of the defence staff, said “all states should redouble efforts to work toward a world without nuclear weapons”.

They said: “We believe the risks posed by nuclear weapons and the international dynamics that could lead to nuclear weapons being used are underestimated or insufficiently understood by world leaders.

“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.

“Stockpiles of the world’s nuclear weapons and materials to produce them are insufficiently secure, making them possible targets for terrorism.”

Other figures who backed the call included former French prime minister Michel Rocard, retired US general James Cartwright, former vice-chairman of the joint chiefs of staff, and delegates from Russia, China and India.

The Vienna conference is due to start on Monday and will last two days. It is estimated 16,300 nuclear weapons, in a potential nine states, still exist in the world.

It comes just weeks after high-level talks between Iran and six western powers missed a deadline for negotiating a deal on its nuclear programme, although it was resolved to extend talks by seven months.

International negotiators are worried that Iran is using its nuclear development programme as a cover for developing weapons, and they have imposed economic sanctions on Tehran.

But Iran denies this, saying it is only interested peaceful nuclear initiatives such as producing power.