“You know, it’s just one firm in one tax haven, and there is much more going on,” Mr. Zucman said, calculating that about 8 percent of the world’s financial wealth is held in tax havens. “So that’s about $7.6 trillion today, a huge amount of wealth.”

It was not immediately clear how Mr. Gunnlaugsson’s decision to step aside would affect Iceland, a tiny island nation of 323,000 that is still recovering from the global financial crisis eight years ago.

In a reflection of the political turmoil and maneuvering that the Panama Papers have created, the prime minister’s office issued a statement on Tuesday night saying that he had proposed stepping down in favor of his deputy “for an unspecified amount of time” — as a sort of indefinite leave of absence — and not a formal resignation. It was unclear whether Mr. Gunnlaugsson, who would remain leader of his party, would succeed in his effort to avoid a formal resignation in the face of significant public anger.

Mr. Gunnlaugsson had insisted on staying in office after the leaked documents revealed that he and his wealthy partner, who is now his wife, had set up the company in the British Virgin Islands in 2007 through Mossack Fonseca. The documents suggested that he sold his half of the company to her for $1 on the last day of 2009, just before a new law took effect that would have required him as a member of Parliament to declare his ownership as a conflict of interest.

Mr. Gunnlaugsson had said that the leak contained no news, adding that he and his wife, Anna Sigurlaug Palsdottir, had not hidden their assets or avoided paying taxes.

But the company, Wintris Inc., lost millions of dollars as a result of the 2008 financial crash, which crippled Iceland, and the company is claiming about $4.2 million from three failed Icelandic banks. As prime minister since 2013, Mr. Gunnlaugsson was involved in reaching a deal for the banks’ claimants, so he was accused of a conflict of interest.