One of Russia's biggest state companies has handed billions of dollars to mysterious private contractors that disguise their ownership or have little or no presence at their registered headquarters, a Reuters investigation has found.

Russian Railways, led by Vladimir Yakunin, an old friend of President Vladimir Putin, awarded about 115 billion rubles ($3.5 billion) to 11 such private companies between 2007 and 2013, according to public tender documents and private bank records.

Two of the 11 firms were the only bidders in 43 tender competitions, worth up to $340 million, since 2010. Though bidding as rivals, the two have striking similarities. They were registered on the same day, opened bank accounts on the same day and in two recent years reported exactly the same number of employees. Of the 11 companies, none of their real owners could be traced, and only one had staff members at its registered headquarters when a reporter visited.