PARIS, April 8 (Reuters) - The United States is starting to resemble an emerging market more than a developed country, the head of pan-European stock exchange operator Euronext said on Tuesday as financial markets remained volatile after the imposition of sweeping U.S. tariffs.

"Fear exists all over," Euronext CEO Stephane Boujnah told France Inter radio. "The country (United States) is unrecognisable and we are living in a transition period. There is a certain form of mourning, because the United States that we had known for the most part as a dominant nation resembled the values and institutions of Europe and now resembles more an emerging market."

Boujnah said investors had been forced to grapple with uncertainty since U.S. President Donald Trump took office in January. "People ... have difficulty understanding the volatility of decisions that are made, so this worry is real, and it is a form of intimidation that diffuses in the system and is difficult to navigate," he said.

Global financial markets are rotating assets and are trying to adapt to a United States that they do not recognise after Trump announced global tariffs on imports to the United States, Boujnah said.

Trump has said the tariffs - a minimum of 10% for all U.S. imports, with targeted rates of up to 50% - would help the United States recapture an industrial base that he says has withered over decades of trade liberalization.

Emerging markets often use tariffs to protect their industries while they try to develop.

Boujnah said there was some good news in that oil prices and long-term rates were down, and that there were flows of money leaving the United States to be re-invested in Europe.

European shares rose in early trading on Tuesday from 14-month lows after four straight sessions of heavy selling, although investors remained sensitive to tariff-related developments, a day after the European Commission proposed counter-tariffs of 25% on a range of U.S. goods. (Reporting by Sudip Kar-Gupta and Makini Brice; Editing by Susan Fenton)