LONDON, July 8 (Reuters) - Copper prices in the United States jumped more than 12% to a record high above $12,330 per metric ton after U.S. President Donald Trump said he would announce a 50% tariff on imports of the metal on Tuesday.

Trump told reporters at a White House cabinet meeting that he planned to make the copper tariff announcement later in the day, but he did not say when the tariff would take effect.

In February, the U.S. launched a probe into the possibility of tariffs on copper imports to help support local production and incentivise investment in new capacity. The deadline for the investigation to conclude is November.

The threat of tariffs on the metal used in the power and construction industries has created a massive premium for copper prices on COMEX above those on the London Metal Exchange, which are currently around $9,585 a ton .

Traders expect the premium - also at a record around $2,750 a ton - to attract more metal to the United States.