Nuclear weapons: Which countries have them and how many are there?

With recent tensions between the US and Iran, you might be hearing a fair bit about nuclear weapons.

They are considered the most destructive weapons in the world - their explosions are so powerful, just one nuclear bomb could destroy an entire city.

Nukes, as nuclear weapons are known, are far more damaging than even the biggest normal, non-nuclear bombs.

There's also been lots of talk about some countries, including Iran, not being allowed to have them, while others can.There's quite a lot to get your head around when it comes to nuclear weapons - but don't worry, we've put together a guide to the key questions.