My sources say that the Russian government issued a demarche to the US State Department following the meteorite explosion over the city of Chelyabinsk on Friday.
The State Dept defines a demarche as "a formal diplomatic representation of one government’s official position, views, or wishes on a given subject to an appropriate official in another government or international organization. Demarches generally seek to persuade, inform, or gather information from a foreign government. Governments may also use a demarche to protest or object to actions by a foreign government."
Chelyabinsk is center of a region known for nuclear research, so until the cause of the Friday event was confirmed as a meteor, does this mean that Russian officials at least considered the possibility of it being some kind of a US action?
Even if they did, the situation did not escalate, but it reinforces long held concerns about natural disasters being misinterpreted as hostile actions.