London Metal Exchange (LME) prices closed firmly on Tuesday, with aluminium near a one-month high on fund buying and supply worries, analysts and traders said.
"There's an obvious desire to push the market higher," Sempra Metals economist John Kemp said.
"However the complex is already too high," he added.
An LME trader said: "We've seen a continuation of CTA buying across the complex and the Ormet news helped firm aluminium."
Ormet Corp said it had to close one of four active potlines at its Hannibal, Ohio, primary aluminium smelter because an impending closure of part of the Ohio River would halt deliveries of alumina.
Ormet said the shutdown would reduce the plant's metal output to 50 percent of its annual 254,000-tonne capacity. The river is to close between August 3 and August 16 and curtailment of production would allow the plant to build a stockpile to allow it to continue operating while river traffic is halted.
Traders said that the real cost of the shutdown would be 30,000-40,000 tonnes of metal.
"The sort of volumes they are talking about are neither here nor there, but it could coincide with a bit of a squeeze," a second trader said.
Aluminium closed at $1,710 a tonne, up from $1,692.50 at Friday's kerb close. Prices peaked at $1,712, the highest since late April.
Copper firmed to $2,817, up $42 on Friday's kerb.
"Copper's holding pretty well. We saw some good US buying this afternoon," the second trader said.
The first trader said: "Funds got short when oil prices spiked last week and now they are covering."
Brokers said expectations of Chinese selling and high energy prices might put pressure on metals.
NYMEX crude futures surged to a record $42.00 a barrel as trading resumed after the holiday weekend amid fears of Middle East supply disruption, dealers said.
Kemp said higher energy prices would have little direct impact on metals, but record oil prices would fuel inflation and result in aggressive interest rate rises leading to a slowing in demand for commodities.
Zinc rose $3.50 to $1,115.50, while lead was up $3 at $836. The cash to three months spread for lead was indicated around $75 backwardation,
Tin closed at $9,350 against $9,000, with the cash to threes backwardation steady at $600. Nickel rose $225 to $12,425, targeting $12,570.