US Federal Reserve Chairman Jerome Powell reacts during a press conference in Washington D.C., the US, on July 31, 2019, when the central bank lowers interest rates for the first time since 2008 financial crisis. (Xinhua/Liu Jie)

US Federal Reserve Chairman Jerome Powell said Friday it is "a new challenge" for the US central bank to fit trade uncertainty into its policy decision-making framework.

"We have much experience in addressing typical macroeconomic developments under this framework. But fitting trade policy uncertainty into this framework is a new challenge," Powell said in prepared remarks at the Kansas City Fed's annual symposium in Jackson Hole, Wyoming.

He stopped short of offering guidance to future policy path, reiterating the pledge that the Fed "will act as appropriate to sustain the expansion."

The market has been eagerly awaiting Powell's interpretation of the Fed's reasoning for future rate moves, as President Donald Trump in recent days ratcheted up criticism against him for not doing enough easing, and Fed officials were split over what convinced them to support a 25 basis point rate cut at the July 30-31 policy meeting.

"Setting trade policy," the central bank chief said, "is the business of Congress and the Administration, not that of the Fed. Our assignment is to use monetary policy to foster our statutory goals" of maximum employment, stable prices and moderate long-term interest rates.

Powell described the three weeks since the July policy meeting as "eventful," beginning with the Trump administration's announcement of new additional tariffs on Chinese imports and presenting "a complex, turbulent picture" of the global economic situation.

"Trade policy uncertainty seems to be playing a role in the global slowdown and in weak manufacturing and capital spending in the United States," he told the event that gathered Fed officials, academics and central bankers from around the world.

While acknowledging that anything that affects the outlook for employment and inflation, including uncertainty in trade policy, could affect monetary policy, Powell said there are "no recent precedents to guide any policy response to the current situation."

"Moreover, while monetary policy is a powerful tool that works to support consumer spending, business investment and public confidence, it cannot provide a settled rulebook for international trade," he said.

Instead, Powell said, the Fed can "try to look through what may be passing events, focus on how trade developments are affecting the outlook," adding that it "will at times be appropriate for us to tilt policy one way or the other because of prominent risks."

The Fed trimmed the federal funds rate by 25 basis points to a target range of 2 percent to 2.25 percent at its July policy meeting, with participants of the rate-setting Federal Open Market Committee citing varying concerns in making the decision, including slowing global growth, the US-China trade dispute and low inflation.

Powell said the Fed will be "carefully watching developments" since the last policy meeting. "Based on our assessment of the implications to these developments, we will act as appropriate to sustain the expansion," he said.

The US economy, he said, is close to the goals of maximum employment and price stability. "Our challenge now is to do what monetary policy can do to sustain the expansion."