Documents from the secretive Panamanian law firm Mossack Fonseca reportedly suggest that major banks have helped well-heeled clients to conceal their money in anonymous accounts around the world. Yet those banks are sometimes denying accounts to clients in poor countries, on suspicion that they might be involved in laundering money, financing terrorism or avoiding taxes, according to experts on the international financial system.

Banks' disparate treatment of suspect financial activity suggests that new regulations in the United States and other developed countries, intended to prevent illicit activity, could be detrimental for charities and some less wealthy economies.

"What the Panama Papers scandal makes really clear is if you’ve got a lot of money, you can get a bank to break more or less any law you want," said Scott Paul, a senior adviser at Oxfam America. "If you don’t have a lot of money, banks will close the door in your face just because of the risk of illegality."

The Washington Post has not reviewed the documents from Mossack Fonesca. Its representatives have said that they did nothing against the law.

For many years, international regulators have worked to make avoiding taxes and funding illicit activity more difficult by getting banks to identify their customers.

Yet since the financial crisis made banking less profitable, some banks have decided that vetting their less affluent, less lucrative customers isn't worth the expense, experts say. In part because of the risk of scrutiny from regulators and the press, firms such as Bank of America and Barclays are now reluctant to do business in poor countries where lawbreaking is more common.

Banks' withdrawal from some markets in East Africa, the Middle East, Latin America and other regions has provoked an international debate about the costs and benefits of authorities' efforts to counter illicit finance.

"Until very recently, there really wasn't a conversation," Paul said. Without careful attention from policymakers, he warned, "it's going to be poor populations and these high-risk jurisdictions that get cut out of the financial system."

Diplomats and charities have lost their accounts. Meanwhile, migrants working in developed countries as breadwinners for their families in poorer nations are paying more to send them money through informal channels. In the private sector and among nonprofit groups, some worry that rules issued by the U.S. government, along with the European Union and a 35-nation body called the Financial Action Task Force, are making the problem worse.

Regulators must balance "restrictions that you want to put in place to keep the bad guys out" against "restrictions so strong that you keep the good guys out, too," argued Rob Rowe, a vice president at the American Bankers Association. "There's no easy answer."

The Obama administration contends that the problem of innocent clients being denied financial services on account of where they do business is limited to a few jurisdictions. Officials say global finance is becoming more interconnected in general, with more money going to developing countries overall. Also, banks might have good reasons for closing their books in some countries, said Adam Szubin, Treasury undersecretary for terrorism and financial intelligence, at a conference last year.

"We recognize that reduced access could impede the flow of money for a family member in need," Szubin said, but he added, "We don't yet see evidence of systemic retrenchment -- and even if we truly are seeing some consolidation, we have not yet identified its scope."

A few cases have made international headlines. Diplomats at the Angolan Embassy in Washington found that Bank of America had closed all of their accounts in 2010, forcing the State Department to intervene. In 2013, Barclays terminated its relationships with about 250 firms that were handling remittances to Somalia, where Oxfam estimates that close to half the population relies on money sent from relatives abroad to meet their basic needs.

Barclays did not say exactly why the accounts were closed, but some experts said the banks were concerned that their customers could be using the money for illicit purposes.

Banks must comply with U.S. and international rules designed to prevent their clients from avoiding taxes, laundering money, circumventing sanctions or financing terrorism. These rules generally require banks to be sure that their customers are who they say they are.

That can be a challenge in the developing world, where many governments don't issue official identification -- and when clients do present documents, tellers might not be able to determine with confidence whether they are genuine or forged, said Liat Shetret of the Global Center on Cooperative Security. She added that local governments might not be much help, depending on their recordkeeping.

Recent regulatory guidance "remains just inapplicable to many of the receiving countries," said Shetret, who previously worked in Citigroup's anti-money-laundering unit.

Then there is the chance that those seeking to launder money or avoid taxes will corrupt banks' employees, noted economist Mike Moebs of Moebs Services, a research firm in Lake Forest, Ill.

"It opens up the internal side of the financial institutions to somebody paying off a teller," he said. "There's always a way."

Treasury officials point out there are other reasons that banks might be closing some clients' accounts.

Interest rates have remained at near zero globally for several years. Also, banks have been required to be more conservative in their lending since the financial crisis. For both these reasons, making loans is less profitable for banks. Some of the accounts they managed in the past might now be losing money.

Whatever the reason, data from the World Bank suggests that financial connections are being broken. In a survey of 20 major international financial institutions published last year, 15 reported they had fewer relationships with banks in foreign countries -- called "correspondent banks" -- than they did three years prior.

Sixteen of the global institutions reported that there were parts of the world in which they had terminated all relationships with their correspondent banks, especially in the Caribbean.

The survey also polled 82 firms that handle remittances. The share reporting that banks had closed their accounts had roughly doubled since 2010. Now, 45 percent say that their agents were unable to access the financial system. Instead, some firms are buying tickets on commercial airliners and sending their employees abroad with suitcases full of cash.

"There is a real risk that turning away customers could actually reduce transparency in the system by forcing transactions through unregulated channels," said Gloria Grandolini, a senior director at the World Bank, in a statement.

It is impossible to know whether the World Bank's data is representative. There are no comprehensive data on the movement of money from banks in rich countries to their counterparties in the developing world.

Yet Tom Keatinge, a former banker at JPMorgan Chase, disputed the Obama administration's more optimistic assessment of the data. He pointed to Syria, where he said that charities are having a hard time getting help to victims of the civil war.

Banks do not want to honor any checks that charities might write to local merchants in exchange for food and supplies, since those merchants could also be violent Islamists, explained Keatinge, who is now at the Royal United Services Institute, the security-research organization in London.

"It looks pretty systematic," he said. "The issue has become so entrenched over the past four or five years."

Angola, meanwhile, is once again dealing with skepticism from international banks. A few months ago, money-laundering concerns reportedly pushed Bank of America, along with Standard Chartered, to announce that they will stop selling dollars to Angolan banks.