The United States has returned documents written by Russia's last tsars and composer Pyotr Tchaikovsky that had been smuggled into the West after the collapse of the Soviet Union.
The documents were spirited out of Russia in the early 1990s - some of them in shipping containers from St Petersburg shipyards - and sent to the United States where they were recovered in New York, Chicago and Atlanta at auction houses.
"You need to remember what ... the 1990s was like. One state ceased to exist and the new state was barely functioning. If it weren't for the investigation, none of these documents would have been returned," said the head of Russia's State Archive agency, Andrei Artizov.
Relations between the United States and Russia have been strained since President Vladimir Putin's return to the presidency last year, and both countries are seeking to improve ties that range from intelligence sharing to cooperation over logistical help as NATO-led forces pull out of Afghanistan.
The documents, returned on Thursday, included handwritten orders by Tsarina Catherine the Great and by the empire's last Tsar Nicholas II, who was deposed by Bolsheviks in 1917.
A personal letter written by Tchaikovsky to 19th century writer Konstantin Zvantsev was also among the papers.
Artizov said U.S. and Russian authorities had worked over the last six years to recover more than 100 historical artefacts that had been smuggled out of Russia in the chaos that followed the fall of the Soviet Union.
He said two criminal cases had been opened into how the documents were stolen from Russian artistic, historical and military archives and that one of the men behind the crime had been identified and was living in Israel.