Copper prices jumped to their highest in nearly three months on Thursday, propelled by a weak dollar, concerns about supply and buying by speculators after key technical levels were broken.

Three-month copper on the London Metal Exchange gained 1.6% to $9,867 a metric ton by 1000 GMT, its strongest since March 28.

"What is key for us is dollar weakness and that is trending lower, which is supportive for our space," said Alastair Munro, senior metals strategist at Marex.

The dollar index sank to its lowest since early 2022 as concerns about the future independence of the U.S. Federal Reserve undermined faith in the soundness of the country's monetary policy.

A softer dollar makes commodities priced in the U.S. currency less expensive for buyers using other currencies.

The premium for the LME cash copper contract over the three-month rebounded to $200 a ton from $101 on Wednesday but down from $280 on Monday, its highest since November 2021.

While traders expect deliveries of copper into LME warehouses to ease a tight situation, they have not yet materialised.

"The market is still positioned short out of July and struggling to find offers this morning," Munro said.

Copper buying was buoyant among Chinese participants, he added, noting that long positions and open interest are rising on the Shanghai Futures Exchange.

The most-traded copper contract on ShFE rose 0.6% to 79,000 yuan ($11,022.74) per ton, its highest since June 11.

LME copper has held below the $9,800 level for several months and a break above there on Thursday triggered automatic buy orders, a trader said.

LME copper has gained 22% since hitting its lowest since November 2023 at $8,105 in April.

U.S. Comex copper futures climbed 2.7% to $5.05 a lb, bringing the premium of Comex over LME copper to $1,277 a ton, its highest since April 28.

Higher U.S. copper prices are based on expectations of U.S. tariffs being imposed on the metal, triggering a flow of metal to Comex warehouses.

Among other metals, LME aluminium rose 0.5% to $2,575 a ton, lead gained 0.6% to $2,044, nickel added 0.8% to $15,190, zinc climbed 1.4% to $2,743.5, while tin rose 0.6% to $33,400. ($1 = 7.1670 Chinese yuan )

(Reporting by Eric Onstad Editing by Frances Kerry)