Updates after Reuters report on Khamenei's uranium position

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 .STOXX fell 0.3%, having risen more than 0.2% earlier in the session.

Futures for the S&P 500 ESc1 fell 0.3% while those for the tech-focused Nasdaq NQcv1 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 =USD, 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 EUR=EBS slipped and was last down 0.1% at $1.161, just above a six-week low.

Brent crude oil LCOc1 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 US10YT=RR, 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.O, the world's biggest company by market capitalisation, were flat in pre-market trading despite the firm's earnings beating Wall Street expectations.

Nvidia on Wednesday forecast second-quarter earnings of $91 billion and announced an $80 billion share repurchase programme.

"Investors want the world from Nvidia," 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.