A coded letter in which Napoleon Bonaparte vows to blow up the Kremlin goes under the hammer near Paris in December, 200 years after the French invasion of Russia.

"I will blow up the Kremlin on the 22nd at three am," reads the missive written in numbers and signed "Nap", expected to fetch between 10,000 and 15,000 euros (13,000 to 20,000 dollars) at the sale in Fontainebleau.

Dated October 20, 1812, the day after Napoleon retreated from the centre of Moscow, it is addressed to his external relations minister Hugues-Bernard Maret.

Napoleon's order was carried out by Marshal Mortier, who destroyed several towers and sections of wall at the Kremlin, at the time both an imperial palace and military fortress. The towers were later rebuilt identically.

"Letters written by Napoleon from Russia are rare," said Alain Nicolas, expert for the auctioneer Ocenat. "Many were lost, probably intercepted by the Russians."

In the letter, currently in private hands, Napoleon asks his minister to gather supplies and to find more horses for his troops, many of which had perished in the freezing weather bearing down on the region.

Another star lot of the sale, an "Essay on campaign fortification" dictated and annotated by Napoleon while in exile on the British island of Saint Helena, the fallen emperor mulls over the outcome of the Russian invasion.

"It should not be called a retreat since the army was victorious," he writes of the campaign, today seen as a turning point in the Napoleonic wars that dramatically weakened French power in Europe.

Napoleon's army entered Moscow on September 14, 1812, but much of the population had already fled and the emperor was forced to leave without securing a formal victory over Alexander I, embarking on a disastrous westward retreat.

"Napoleon argued that the Russian winter was his sole victor, insisting the campaign would have gone differently had it taken place three months earlier," explained the auction house.

"While in exile on Saint Helena, Napoleon kept endlessly mulling over his battle and military strategy, dictating to the loyal General Bertrand," added Jean-Christophe Chataignier, head of Empire department at the house.

The "Essay", which comes from General Bertrand's family, is part of a lot of 180 double-sided manuscript pages and 44 sketches, dated between July 1818 and August 1819 and estimated at 60,000 to 80,000 euros.