LONDON — Six weeks after the Panama Papers revealed vast stores of hidden offshore wealth around the world, leaders from Britain, the United States, and other nations vowed Thursday to cooperate on sweeping measures against financial corruption.

At a conference in London, Britain’s prime minister, David Cameron, who two days earlier was overheard describing Afghanistan and Nigeria as “fantastically corrupt,’’ announced measures to clamp down on money laundering in his own country.

He put forth proposals to make offshore companies that buy property in Britain reveal their true ownership, forcing those that hide behind complex financial structures to accept transparency. The same provisions would apply to firms that already own property in the country and to those bidding for British government contracts.

Secretary of State John Kerry, representing the United States, condemned financial corruption as a threat to democracy.

The hiding of assets from tax authorities harms people around the world by depriving governments of the resources they need to provide health care, build schools, and invest in infrastructure, he said.

Afghanistan, Nigeria, France, and the Netherlands pledged Thursday to set up their own public registers of true company ownership.

New York Times