A French auction house Monday sold a historic Chinese seal for 1.1 million euros ($1.4m) despite threats of legal action alleging it may have been stolen from Beijing's Forbidden City in 1860.

The green jade seal, which dates from the Qianlong period (1736-95) and had been expected to fetch up to 200,000 euros ($263,000), went for over five times that amount to an unidentified telephone bidder.

The Association for the Protection of Chinese Art in Europe (APACE) had urged auction house Artcurial to withdraw it from the sale saying it was stolen in 1860 when the Summer Palace was pillaged by Anglo-French troops.

Artcurial says in its catalogue that the seal, 2cm high by 4.5cm long, comes from the personal collection of a French family which has owned it since the end of the 19th century.

"According to Kai Shan Yyan, the former curator of the Palace Museum, this seal could have belonged to emperors of the Qing dynasty and could have been stolen during the sacking of the Summer Palace," APACE said.

The group said it had already mandated a lawyer to "take all legal action", including filing a criminal complaint for theft and receiving stolen goods, if the sale went ahead.

"This piece is an integral part of Chinese heritage," APACE said, adding that not "only Chinese authorities but the whole of China would be grateful" if the seal was withdrawn from auction.

The Old Summer Palace, or Yuanmingyuan, was pillaged by a joint British and French military expedition during the second Opium War on October 18-19, 1860.

The event is seen as a national humiliation at the hands of Western armies, and every anniversary of the destruction of this "wonder of the world" -- as French writer Victor Hugo described it -- gives rise to a nationalistic push.

Beijing estimates that at least 1.5 million relics were pillaged by the armies.

Relics stolen from the resort -- bits of porcelain, enamel, sculptures, furniture, silk paintings -- were legally sold long after the raid.

Two such items are bronze fountainheads that belonged to late French fashion designer Yves Saint Laurent and his partner Pierre Berge were auctioned for 31 million euros in a move that angered China but the successful bidder then refused to pay up.