New Delhi, Dec. 24 -- Copper prices crossed the $12,000-a-ton mark for the first time, extending their recent rally as mine disruptions heightened worries over the supply of the crucial industrial metal.

On Tuesday, copper prices on the London Metal Exchange rose as much as 2% to $12,159.50. Copper has surged over 35% so far this year and is heading for its strongest annual gain since 2009.

The possibility of US import tariffs on the metal has been a key driver behind this year's price rise. Copper inventories are building up in US warehouses as the prospect of fresh duties encourages buyers to lock in supplies and has created opportunities for arbitrage trades, according to a Bloomberg report.

Supply concerns that had lingered for yea...