Powell said trade uncertainties and concerns about the global economy continue to weigh on the U.S. economic outlook and the U.S. central bank stands ready to "act as appropriate" to sustain a decade-long expansion.
Markets jumped on the comments as sufficiently dovish pushing the S&P 500 above the 3,000 mark for the first time and sending most European indices into positive territory.
The optimism was however, short-lived with all major indices slipping back into negative territory and the pan-European index STOXX 600 <.STOXX> closing 0.2% lower.
"So far the central banker hasn't given much away in terms of clues as to possible changes to monetary policy, although earlier in the day, he warned that uncertainties have continued," said David Madden, market analyst at CMC Markets.
"Some dealers are sitting on their hands until they get a clear view from Powell."
Powell's statements on the global economy come a day after German chemical giant BASF warned that the protracted trade war between the United States and China was likely to eat into corporate earnings, in particular for the agricultural and auto sectors.
Bond proxies such as real estate <.SX86P> and telecom <.SXKP> were the biggest losers but banks <.SX7P> and Milan's bank-heavy FTMIB index <.FTMIB> outperformed as robust industrial data out of France and Italy earlier in the day helped push euro zone bond yields higher.
A surge in crude prices and gains for metals helped energy and mining majors helped the oil and gas <.SXEP> and basic resources <.SXPP> sectors gain nearly 0.6% each.
Chip stocks led by AMS also fared better after TSMC reported its best monthly sales in June since December.
Planemaker Airbus rose 1.5% after confirming deliveries rose by 28% in the first-half of the year, putting it ahead of Boeing for the first time in eight years.
Among individual losers, British recruiter Hays Plc was down 6.6% as peer Pagegroup tumbled 15% after issuing a profit warning, while fashion retailer Superdry slid on posting disappointing full-year results.
(Reporting by Agamoni Ghosh, Susan Mathew and Amy Caren Daniel in Bengaluru; Editing by Arun Koyyur and Frances Kerry)
By Agamoni Ghosh