A 1963 treaty prohibiting the testing of nuclear weapons in any part of the world–up to the atmosphere, the oceans and space. This was originally put forward by the US, the former USSR and the UK. The impact of the treaty has been diminished, however, as it was boycotted by nuclear nations France and China. All 5 nuclear nations signed a Comprehensive Test Ban Treaty in 1996. There have been problems with enforcement, as Iran and North Korea have defied the test-ban, recently conducting nuclear tests in their own countries.