* S&P 500, Nasdaq end lower

* Oil prices gain as Iran worries continue

* Longer-dated U.S. Treasury yields off recent highs

(Updates with oil settlement, S&P 500 and Nasdaq closing lower)

By Caroline Valetkevitch and Samuel Indyk

NEW YORK/LONDON, May 18 (Reuters) - Major stock indexes

mostly eased as technology shares fell on Monday, while oil

prices climbed following continued worries over supply

disruption from the Iran war.

Longer-dated U.S. Treasury yields were nearly flat after

climbing to their highest level in over a year in overnight

trading.

Sovereign bond yields have risen sharply recently as investors

worry the war in Iran that began in late February may bring a

lasting inflationary shock.

President Donald Trump posted on social media on Monday that

he was holding off on a planned military attack on Iran

scheduled for Tuesday, while efforts continue to reach a deal.

He added that the United States was ready to resume attacking if

one is not reached.

U.S. crude rose $3.24 to settle at $108.66 a barrel,

while Brent crude gained $2.84 to $112.10.

Investors are also focused on the tech sector's recent sharp

gains and are bracing for results from Nvidia ( NVDA ) this

week.

Technology, down 1%, led sector declines in the

S&P 500, while an index of semiconductors was down 2.5%.

Energy led sector gainers and was last up 1.8%.

Trump's recent trip to China "left a lot of open questions

about the future of Taiwan and whether or not the United States

would be there to protect it," said Oliver Pursche, senior vice

president, advisor for Wealthspire Advisors in Westport,

Connecticut.

"Given Taiwan's significance to the chip market, that

partially explains the selloff we're seeing in that sector

today," he said, adding that investors are also taking profits.

Trump's first visit to Beijing since 2017 ended on Friday with

no major breakthroughs on trade or tangible help from Beijing to

end the U.S.-Israeli war on Iran.

The Dow Jones Industrial Average rose 159.95 points,

or 0.32%, to 49,686.12, the S&P 500 fell 5.45 points, or

0.07%, to 7,403.05 and the Nasdaq Composite fell 134.41

points, or 0.51%, to 26,090.73.

MSCI's gauge of stocks across the globe fell

0.24 points, or 0.02%, to 1,098.76. The pan-European STOXX 600

index rose 0.54%.

Rising yields push up borrowing costs and mean a higher

discount for future company earnings, challenging stock

valuations.

The yield on the benchmark 10-year Treasury note

climbed to 4.659% in overnight trading, its highest level since

February 2025. It has since retraced its gains and was last flat

on the day at 4.591%.

Earlier, Japan's 10-year yield hit a peak not seen since

1996 as the government proposed to issue fresh debt to fund a

planned extra budget to cushion the economic blow from the Iran

war. Germany's 10-year bond yield rose to a

level not seen in 15 years.

AI, RETAIL EARNINGS TO TEST STOCKS' RECENT RALLY

The artificial intelligence trade will be tested by earnings

from Nvidia ( NVDA ) that are due on Wednesday, with

expectations sky-high for the world's most valuable company.

Nvidia ( NVDA ) shares are up sharply since a March low, while the

Philadelphia SE semiconductor index has also surged amid

demand for chips as tech companies spend massively to build

AI-related infrastructure.

Also due this week are results from a host of retailers,

including Walmart ( WMT ), which will provide an insight into

how consumers are faring with high energy prices.

The dollar slipped against most major currencies as U.S.

Treasury yields were off recent high levels.

The dollar index, which measures the greenback

against a basket of currencies including the yen and the euro,

fell 0.33% to 99.03.

Spot gold rose 0.31% to $4,552.19 an ounce.