British Prime Minister David Cameron has been caught on microphone saying that leaders of "fantastically corrupt" countries including Nigeria and Afghanistan will attend an anti-corruption summit in London.

Cameron will bring together politicians and officials from around the world Thursday as part of efforts to clamp down on bribery, money laundering and other forms of wrongdoing.

At a Buckingham Palace reception Tuesday, a television microphone caught Cameron saying "we have got some leaders of some fantastically corrupt countries coming to Britain."

He referred to "Nigeria and Afghanistan — possibly two of the most corrupt countries in the world."

Nigerian President Muhammadu Buhari and Afghan President Ashraf Ghani — both elected in 2014 — have promised to curb corruption in their countries. Both are due to attend Thursday's meeting in London.