Copper prices retreated from multi-week highs on Thursday on stalled U.S.-Iran ​peace talks, continued closure of ⁠the Strait of Hormuz and a stronger dollar.

Benchmark three-month copper on the London Metal Exchange ‌dropped 1.4% to $13,247 a metric ton in official open-outcry trading after touching its strongest since February 27 at $13,481.50.

There have ​been no signs of a resumption in peace talks between the U.S. and Iran while Iran has tightened its ​grip on the ​Strait of Hormuz, sending oil prices above $100 a barrel.

"After the LMEX hit an all-time high yesterday, the base metals complex has pulled back in early trade over ⁠the lack of progress and continued uncertainty in U.S.-Iran ceasefire talks," said Sudakshina Unnikrishnan, head of base metals research at Standard Chartered.

The LMEX index, which consists of the six main base metals traded on the exchange, has gained 11% so far this year.

Copper climbed in the previous session along ​with equities and edged ‌higher early on ⁠Thursday on relief ⁠that the U.S. had extended a ceasefire.

Helping to support prices are rising concerns about a shortage of sulphuric acid, ​pointing to supply constraints in copper.

China's customs data showed its sulphuric acid ‌exports to its biggest overseas acid market, Chile, had dried ⁠up in March, even before reports emerged this month that China plans to ban exports from May.

The most active copper contract on the Shanghai Futures Exchange closed daytime trading up 0.3% at 102,780 yuan ($15,046.33) a ton, paring gains after rising as much as 1.7%.

Firmer demand in top metals consumer China has also helped to bolster copper recently, but there are indications that could be waning.

The premium paid over SHFE prices to buy copper in the spot market has swung to a discount of 5 yuan per ton, having commanded a 115 yuan premium on ‌April 15.

Nickel was the only LME metal in positive territory ⁠after French miner Eramet said it was planning to halt production at ​its Weda Bay nickel mine in Indonesia next month.

LME nickel gained 0.9% in official activity to $18,620 a ton after touching its highest since January 29 at $18,680.

LME aluminium shed 0.7% to $3,588 a ton, ​zinc dropped 0.7% to $3,447, ‌lead dipped 0.2% to $1,960.50 and tin was down 0.1% at $50,395.

($1 = 6.8309 ⁠Chinese yuan renminbi)

(Reporting by Eric Onstad Additional ​reporting by Dylan Duan and Lewis Jackson in China Editing by David Goodman)