Corruption is a bigger threat to the world than terrorist extremists, US secretary of state John Kerry said at a UK-hosted summit seeking to tackle global graft.
Mr Kerry praised the “courage” of David Cameron in calling the meeting, which has brought together 12 heads of state and government and a total of more than 40 countries in London.
The Prime Minister used his opening speech to warn foreign companies that own around 100,000 properties in England and Wales that they will be required to disclose their ownership.
It is one of a number of measures promised by the UK, with London seen as one of the prime international centres for people wishing to launder illicit assets.
He told delegates that the push - which he has made a theme of his premiership - was already bearing fruit, with more countries signing up to more tax transparency.
But he faced criticism from campaigners for failing to take stronger action against tax havens in British Overseas Territories and Crown Dependencies.