8. North Korea
Estimated Warheads: Fewer than 10
First Test: 2006
Most Recent Test: 2013
Total Tests: 3
Experts say the country has plutonium for about 10 warheads, but it is not thought to have the technology to deliver the weapons, the report states.
North Korea has conducted three underground nuclear tests, with the most recent coming in February. It has also carried out ballistic missile tests. But it is not thought to have brought the two technologies together yet, the report adds.