A direct attack by Russian forces on American or British troops in Afghanistan would be seen an act of war.
But the use of a proxy militia to achieve the same end adds a layer of ambiguity and deniability.
It places such activity in a grey zone of actions designed to cause harm or achieve an advantage against an opponent but not to trigger all-out conflict.
That is what Russia’s military intelligence agency is accused of doing in Afghanistan by offering bounties to Taliban-linked militants for killing UK and other NATO forces.
Moscow dismissed the claims as “fake news”. But British and European security officials say the US intelligence analysis is “credible”.
It is being shared with a number of European capitals, including London.
How governments respond will be important, particularly at a time when certain parts of the European Union, led by France, are keen to rebuild ties with Russia.
President Emmanuel Macron said on Twitter on Saturday that he would travel to Russia soon for another round of dialogue with President Vladimir Putin.
The pair spoke via video conference on Friday in what the French leader described as “trust-building talks”.
As well as the alleged Afghan operation, Russia’s GRU intelligence agency is accused of the Salisbury spy poisoning, an attempted coup in Montenegro and the poisoning of a Bulgarian arms dealer.
It is part of a pattern of activity that analysts say is designed to undermine Western alliances such as the EU and NATO and to punish those regarded by the Kremlin as traitors.
“I don’t buy this idea that Putin’s a strategic genius,” said Arthur Snell, a former British diplomat who now works as a managing director at Orbis Business Intelligence, a private intelligence company in London.
“He’s got a rather limited zero-sum approach. You could argue he’s slightly gone down a rabbit hole where anything that is bad for the West, NATO, US, UK, is good for him.”