warhead

Even so, the two sides were careful not to abandon the caps in nuclear forces, which limits each side to no more than 1,550 deployed nuclear warheads.

He argued that "stopping Russia now" was cheaper than "wondering who will be the first to create a simple drone carrying a nuclear warhead".

The lack of warheads on the Gerberas drones employed on Wednesday make them appear less threatening and allow Russia to play down the action, Mr Crump added.

In January, North Korea claimed to fire a new intermediate-range ballistic missile tipped with a hypersonic warhead, which it said "will reliably contain any rivals in the Pacific region".

These are "dual-use weapons", meaning their warhead can be either nuclear or conventional high explosive.