The white jade imperial seal, which Beijing says was looted from the Summer Palace in 1860, was acquired by a Chinese national who refused to give his name, telling reporters he was acting on behalf of an art collector in France.

Sold as part of a collection of Asian art, the seal went for more than five times its estimated price of 300,000 euros, after a tense bidding race with another Asian buyer in a packed auction room.

The authorities that manage Beijing's Summer Palace, former home to China's Qing Dynasty (1644-1912) emperors, issued a sharp protest over the sale, saying the seal was looted by British and French forces in 1860.

'Such relics should all be repatriated to China and returned to their place of origin,' the Beijing palace authority said in a statement.

'We once again express strong indignation at this sort of repeated action that hurts the Chinese people's feelings, harms their cultural interests, and violates relevant international pacts,' it said.

Mounted with two carved dragons back to back, the seal comes from the personal collection of a descendant of Elie Jean de Vassoigne, a French general who commanded some of the invading troops.

The 10-centimetre piece bears an inscription reading 'peace and tranquility to the nation.'

Thierry Portier, auctioneer at Beaussant-Lefevre which organised the sale, said there was no reason not to go ahead.

According to Portier, a dozen Chinese imperial seals are sold each year across the world, with one 17th-century piece snapped up in southern France last year for 5.6 million euros, without drawing complaints from China. -- AFP