Updates prices at 1415 GMT, adds fresh Iranian news, aluminium inventories

By Eric Onstad

LONDON, May 21 (Reuters) - Copper prices eased on Thursday after another obstacle emerged to the U.S. and Iran forging a peace deal and from worries about the risk of weaker metals demand from a prolonged conflict.

Benchmark three-month copper CMCU3 on the London Metal Exchange fell 1.1% to $13,504.50 a metric ton by 1415 GMT after climbing by 1.8% in the previous session.

LME copper has gained 8% this year but has pulled back from the $14,196.50 touched last week for its highest in more than three months.

"For now, geopolitics is setting the tone; but without a clear demand catalyst, copper is struggling to hold on to record-high momentum," said ING commodities strategist Ewa Manthey.

Oil prices jumped after Reuters reported that Iran's Supreme Leader has issued a directive that the country's near-weapons-grade uranium should not be sent abroad, which could complicate talks on ending the war. O/R

Investors are trying to balance the impact of potential supply tightness because of mine disruptions and shortages of sulphuric acid against the threat of eroding demand owing to higher inflation and weaker economic growth.

"The base metals market remains wary of demand losses stemming from elevated energy prices and the conflict’s implications for global growth and inflation," said Standard Chartered analyst Sudakshina Unnikrishnan.

LME aluminium CMAL3 added 0.6% to $3,644.50 a ton, helped by the buying of options by bullish investors betting on further disruptions in the Gulf. The region accounts for about 8% to 9% of global output.

Tight conditions are being highlighted by a 33% slide in LME aluminium inventories MALSTX-TOTAL so far this year to their weakest since October 2022.

LME nickel CMNI3 fell 0.8% to $18,770 a ton as investors absorbed details of a new Indonesian policy to place exports of some nickel products under state control.

Zinc CMZN3 fell 1% to $3,519.50 a ton, lead CMPB3 nudged 0.6% higher to $1,992 and tin CMSN3 dropped 1.1% to $53,450.