(Updates after Reuters report on Khamenei's uranium position)

* European stocks and U.S. futures fall

* Supreme Leader says uraniam should stay in Iran

* Stance could threaten U.S.-Iran peace talks

* Nvidia ( NVDA ) stock slips despite earnings beating forecasts

By Harry Robertson

LONDON, May 21 (Reuters) - European stocks and U.S.

futures fell on Thursday as oil prices rose after Reuters

reported Iran's Supreme Leader has said the country's

near-weapons-grade uranium should not be sent abroad, a hard

stance against one of the main U.S. demands.

Europe's STOXX 600 index fell 0.3%, having risen more

than 0.2% earlier in the session.

Futures for the S&P 500 fell 0.3% while those for

thetech-focused Nasdaq dropped 0.4%.

Ayatollah Mojtaba Khamenei's order could complicate talks

on ending the U.S.-Israeli war on Iran, potentially making the

conflict, which has sent energy prices soaring, drag on.

U.S. President Donald Trump has assured Israel that Iran's

stockpile of highly enriched uranium will be removed and that

any peace deal must include the demand, Israeli officials have

told Reuters.

The index tracking the U.S. dollar, which has been a

safe haven for investors during the war, rose following the

Reuters report and was last up 0.1% at 99.23.

The euro slipped and was last down 0.1% at

$1.161, just above a six-week low.

Brent crude oil climbed and was last 2% higher at

$107 a barrel.

Investors in the U.S. and Europe on Thursday were also left

mulling mixed messages from Trump on Iran.

The U.S. president said on Wednesday he could wait a few days

for "the right answers" from Tehran, which helped Wall Street

stocks rally, but was also willing to resume strikes on the

country.

Pakistan was stepping up diplomatic efforts to keep U.S.-Iran

peace talks on track, as officials in Tehran said they were

reviewing Washington's latest responses.

"Conviction is lower this time," said Francesco Pesole,

currency strategist at ING. "Rhetoric from both sides remains

belligerent, and markets are more hesitant to chase optimistic

headlines after earlier disappointments."

U.S. 10-year Treasury yields, which set the tone

for borrowing costs around the world, rose along with oil prices

and were last trading 3 basis points higher at 4.601%.

They hit a 16-month high of 4.687% on Tuesday as traders

continued to scrap their previous bets on Federal Reserve rate

cuts.

Shares in Nvidia ( NVDA ), the world's biggest company by market

capitalisation, were flat in pre-market trading despite the

firm's earnings beating Wall Street expectations.

Nvidia ( NVDA ) on Wednesday forecast second-quarter earnings of $91

billion and announced an $80 billion share repurchase programme.

"Investors want the world from Nvidia ( NVDA )," said Dan Coatsworth,

head of markets at AJ Bell.

"Despite the company once again beating consensus quarterly

sales and earnings estimates, the shares fell in pre-market

trading on worries around the sustainability of its rapid

growth."

Questions about the durability of the AI rally have failed

to dent the massive rise in U.S. stocks, however, which are up

more than 8% this year.