By Ryan Tracy, Victoria McGrane and Andrew Ackerman 

The ripple effect of wild swings in the price of Switzerland's currency is a reminder the next threat to today's highly interconnected financial system could come from an unexpected place.

The sudden decision by the Swiss National Bank on Thursday to remove a cap on the Swiss franc's value posed a threat to the solvency of currency brokers, many of whom sit outside the banking system that has received the brunt of new regulations since the 2008 financial crisis. The market volatility also spilled over into losses at big global banks that trade in currencies as a core part of their business, such as Citigroup, Inc., Deutsche Bank AG and Barclays PLC. Citigroup also provided prime brokerage services to a large U.S. currency broker caught up in the volatility, FXCM, Inc.

Regulatory officials said Friday they didn't see any immediate threats to U.S. financial stability. U.S. agencies were talking among themselves and to market participants as they sought to understand the extent to which big banks, clearing houses that guarantee some currency trades and other market players are exposed to the troubled brokerages or to the currency itself, and how their actions could ripple across the financial system in unexpected ways.

Spokesmen for the Securities and Exchange Commission and Commodity Futures Trading Commission said their agencies were "monitoring" developments. Staff of the Financial Stability Oversight Council, a group of senior U.S. regulators, were also watching the situation, a person familiar with the matter said Friday. A spokeswoman for the Treasury Department, which chairs the council, declined to comment.

At the Federal Reserve, officials are looking into losses major global banks are taking and likely investigating whether any highly-leveraged hedge funds have found themselves on the wrong side of a trade that could trigger broader consequences. Another area of potential focus is how the various firms that operate the financial plumbing for foreign-exchange and other markets are reacting to events.

The Fed created a new postcrisis Office of Financial Stability Policy and Research in 2010 to investigate weak links in the financial system.

One mitigating factor from a financial stability standpoint is that the Swiss action didn't come amid broader market turmoil.

The events were a "reminder [of] how dependent market stability is on government action and how even one seemingly small move can unsettle everything really quickly," said Karen Shaw Petrou, managing partner of the policy analysis firm Federal Financial Analytics, Inc.

Regulators say the financial system is stronger thanks to the reforms implemented since 2008, in particular rules that forced the largest, most interconnected banks to maintain far higher levels of capital to absorb unexpected losses.

"Significantly more capital in banks is a good thing and they're likely to be more resilient," former Federal Reserve Governor Jeremy Stein said in an interview with The Wall Street Journal earlier this week. "There's less worry, I would say, about the banking system being at the center of something."

But Mr. Stein and others acknowledge that by bulletproofing banks' balance sheets, policy makers may be pushing activity outside the banking system into areas where risks are more difficult to monitor.

In the interview, Mr. Stein pointed to the "very, very rapid growth of issuance of corporate bonds" held by nonbank entities as one area where potential risks should be investigated.

The events of Thursday and Friday put activities by less-heavily regulated exchange brokers on regulators' radar as well. Capital requirements for those firms aren't as high as for banks, meaning they are less able to weather unexpected losses.

Another potential area of concern is that capital rules for foreign-exchange brokers don't currently exist in Europe, where regulators have consistently lagged behind their U.S. counterparts on postcrisis rules.

While European policy makers have floated proposed rules, they would likely revisit them in light of the FXCM tumult, said Bart Chilton, a senior policy adviser at DLA Piper LLP and former CFTC commissioner.

One of the key reforms of the 2010 Dodd-Frank law was to move trading in relatively opaque financial products, like derivatives, onto centralized clearinghouses, which take fees to guarantee trades and force traders to post collateral known as margin. The potential downside: Those clearinghouses have become increasingly important parts of the financial system, meaning that their own actions could have broad ripple effects.

Banks and others have raised concerns with regulators that clearinghouses now pose a new threat to financial stability and have called for actions to beef up their resiliency. The Financial Stability Oversight Council is probing the issue in an effort to evaluate what risks clearinghouses might pose.

Write to Ryan Tracy at ryan.tracy@wsj.com, Victoria McGrane at victoria.mcgrane@wsj.com and Andrew Ackerman at andrew.ackerman@wsj.com

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