"China 'firmly opposes and strongly condemns' an auction house in the UK," after it refused to stop the sale of an "illegally-discharged cultural relic," according to a statement issued by China's State Administration of Cultural Heritage on Tuesday.

The "Tiger Ying," a bronze relic which was looted from Beijing's Old Summer Palace in 1860, was discovered in the UK, and is set to go under the hammer at the Canterbury Auctions Gallery on April 11, 2018, with an estimated value price of 120,000 to 200,000 pounds.

Chinese authorities are calling on those involved to adhere to international conventions and halt the upcoming sale.

However, the Canterbury Auctions Gallery has issued its own statement, saying "Tiger Ying" will go up for auction as planned.

"The State Administration of Cultural Heritage will closely follow development of the incident, and will promote the return of illegally-discharged cultural relics by all necessary means in accordance with relevant international conventions and Chinese laws," reads the statement.

The ancient bronze cup is believed to date back some 2,000 years. Authorities believe it was taken by British soldiers when a a multi-nation coalition invaded Beijing during the Boxer Rebellion and looted the old Summer Palace.