By Carolina Mandl

NEW YORK Hedge funds increased their bearish bets mainly on U.S. stocks last week when the major stock indexes plunged, Goldman Sachs showed in a report.

The bank said its clients mostly added short positions while also getting rid of long positions. Among sectors, consumer discretionary, industrials and financials were the most net sold.

"Hedge funds have been pressing U.S. shorts in five of the past six weeks, and this week's notional short selling was the largest since Sept. 22," Goldman Sachs' prime brokerage team wrote.

Hedge funds added short positions mainly in so-called macro products, including equity index and exchanged-traded funds, the bank said.

Since the beginning of the year, short flows in U.S. stocks are up over 20%, another Goldman report showed.

Goldman Sachs, as one of the biggest providers of lending and trading services through its prime brokerage unit, is able to track hedge funds' investment trends.

After a tumultuous week for stocks as Treasury yields hit 16-year highs, all three major U.S. stock indexes posted weekly losses, with the S&P 500 and the Nasdaq registering their largest Friday-to-Friday percentage drops since March.

Goldman Sachs also said hedge fund managers decided to unwind risk last week, mostly by selling long equity positions. "This week's notional de-grossing activity in Japan – long and short combined – was the largest since Dec. 21," the bank said.

The Bank of Japan maintained ultra-low interest rates on Friday and its pledge to keep supporting the economy until inflation sustainably hits its 2% target.

(Reporting by Carolina Mandl in New York; Editing by Richard Chang)