U.S. Federal Reserve Chair Janet Yellen said on Friday that any changes to the post-crisis financial reforms should be "modest" as these reforms have made the financial system substantially safer and resilient.

"The balance of research suggests that the core reforms we have put in place have substantially boosted resilience without unduly limiting credit availability or economic growth," Yellen said at an annual central bank research conference in Jackson Hole, the U.S. state of Wyoming, adding the more resilient financial system is better prepared to absorb, rather than amplify, adverse shocks.

Therefore, "any adjustments to the regulatory framework should be modest and preserve the increase in resilience at large dealers and banks associated with the reforms put in place in recent years," Yellen told central bankers and researchers at the symposium sponsored by the Federal Reserve Bank of Kansas City.

Yellen also warned that policymakers should not ignore the lessons from the recent financial crisis in 2008 that hit the U.S. economy and households hard, as "we can never be sure that new crises will not occur."

"If we keep this lesson fresh in our memories -- along with the painful cost that was exacted by the recent crisis -- and act accordingly, we have reason to hope that the financial system and economy will experience fewer crises and recover from any future crisis more quickly, sparing households and businesses some of the pain they endured during the crisis that struck a decade ago," she said.

Yellen's remarks come as the Trump administration prepares to roll back some tough financial regulations during the Obama administration. U.S. President Donald Trump has made deregulation a key part of his financial agenda and repeatedly blamed the 2010 Dodd-Frank Act, which was designed to prevent another financial meltdown, for stifling economic growth.

Yellen's latest warning on financial deregulation might reduce her possibility of serving a second four-year term as head of the central bank. Her current term will expire in February.

In an interview with the Wall Street Journal last month, Trump said Yellen and the White House National Economic Director Gary Cohn are among contenders to lead the central bank next year.

But Trump said he probably wouldn't announce his nominee for next Fed Chair until the end of this year, as it's still early to make that decision.

Yellen didn't mention U.S. monetary policy in her remarks.

Most economists expect the Fed to begin shrinking its balance sheet in September, with a further rate hike in December, according to the latest survey conducted by the Wall Street Journal.