U.S. Secretary of State John Kerry says corruption is a global "pandemic" and as big a threat to nation states as terrorism.

Kerry has told an international anti-corruption summit in London that as the United States' top diplomat, "I've been shocked by the degree to which I have found corruption pandemic in the world today."

He says that "corruption writ large is as much of an enemy, because it destroys nation states, as some of the extremists we're fighting."

British Prime Minister David Cameron has gathered leaders, civil-society groups and representatives of banks and financial institutions at Thursday's conference with the goal of producing a strong global declaration against financial wrongdoing.