For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window

Updates after markets open

By Lisa Pauline Mattackal and Purvi Agarwal

April 17 (Reuters) - The S&P 500 and the Nasdaq rose on Thursday on the final trading day of the week, with focus on U.S.-Japan tariff talks, while a slump in UnitedHealth's shares following a forecast cut by the insurer weighed on the Dow.

After steep losses on Wednesday, investors found some optimism from U.S. President Donald Trump's comments on "big progress" in trade talks with Japan.

Focus will be on negotiation talks with dozens of countries over the coming weeks for more clarity on the size and scope of tariffs on individual nations and sectors.

Meanwhile, UnitedHealth UNH.N plummeted 17.2% after lowering its annual profit forecast on expectations of high medical costs for the rest of the year.

Other health insurers slumped, with CVS Health CVS.N down 6.1% and Humana HUM.N falling 6.4%.

At 09:35 a.m. ET, the Dow Jones Industrial Average .DJI fell 517.74 points, or 1.31%, to 39,151.65, the S&P 500 .SPX gained 9.48 points, or 0.18%, to 5,285.18, and the Nasdaq Composite .IXIC gained 17.33 points, or 0.09%, to 16,324.63.

Healthcare shares .SPXHC led sectoral declines, but losses were limited by a 13% gain in Eli Lilly LLY.N. The drugmaker said its experimental pill, orforglipron, led to weight loss of nearly 8% and lowered blood sugar in type 2 diabetes patients.

The CBOE Volatility index .VIX was down from last week's highs, but sharply above its 50-day moving average. It was last down 1.22 points to 31.42.

Data showed weekly jobless claims came in lower-than-expected, suggesting the labor market remains stable.

"We don't know how far Trump will let the market fall to achieve his endgame, until we have some clarity I would expect markets to continue to be very choppy," Ross Bramwell, market strategist at Homrich Berg, said.

Indexes had extended losses on Wednesday after U.S. Federal Reserve Chair Jerome Powell warned Trump's trade policies risked pushing inflation higher while weakening economic growth, adding policymakers needed more clarity before adjusting policy.

Trump hit back on Thursday, saying in a Truth Social post that Powell's termination "cannot come fast enough" and calling for the U.S. central bank to cut interest rates.

Traders have scaled back bets of a May rate cut to 13.6%, according to CME's FedWatch, and a Reuters poll showed economists see a higher probability of a U.S. recession in the next 12 months.

Ahead of the long weekend, all three major Wall Street indexes are on track for weekly losses, with the S&P 500 .SPX on pace to lose about 1.6% after its best week since November 2023.

Upbeat results from Taiwan Semiconductor Manufacturing Co (TSMC) 2330.TW helped ease some gloom for the chip sector, after Nvidia NVDA.O flagged steep costs from new U.S. export curbs. TSMC's U.S.-listed shares TSM.N gained 2.5%.

Netflix NFLX.O is scheduled to report results after the closing bell.

Advancing issues outnumbered decliners for a 2.58-to-1 ratio on the NYSE and a 1.88-to-1 ratio on the Nasdaq.

The S&P 500 posted no new 52-week high and two new lows, while the Nasdaq Composite recorded nine new highs and 39 new lows.

(Reporting by Lisa Mattackal and Purvi Agarwal in Bengaluru; Editing by Shinjini Ganguli and Shounak Dasgupta)

((LisaPauline.Mattackal@thomsonreuters.com))