By Steven Eke
BBC Russia analyst
A new Russian law, adopted earlier in the year, formally permits the extra-judicial killings abroad of those Moscow accuses of "extremism".
In the wake of the death of ex-spy Alexander Litvinenko in London, the Sunday Telegraph has alleged that Russian spy agencies - "emboldened" by the new law - have carried out a number of such targeted killings.
In July, the upper chamber of the Russian parliament - the Federation Council - approved a law which permits the Russian president to use the country's armed forces and special services outside Russia's borders to combat terrorism and extremism.
At the same time, amendments to several other laws, governing the security services, mass media and communications, were adopted.
The overall result was to dramatically expand those defined as terrorist or extremist.
Along with those seeking to overthrow the Russian government, the term is also applied to "those causing mass disturbances, committing hooliganism or acts of vandalism".
Much more controversially, the law also defines "those slandering the individual occupying the post of president of the Russian Federation" as extremists.
Russian lawmakers insisted that they were emulating Israeli and US actions in adopting a law allowing the use of military and special forces outside the country's borders against external threats.
But the Russian law is very specific in that it permits the president - alone, and apparently without consultation - to take such a decision.
Protesters against the law wrote an open letter to Mr Putin
The only proviso is that he must inform the Federation Council within five days.
At the same time, he is not obliged to disclose the location of the operation, which units are involved, or the timescale for its execution.
Memorial, one of the oldest and most-respected Russian human rights groups, reacted strongly to the new law.
In an open letter addressed to Vladimir Putin, it accused the Russian leader of sanctioning extra-judicial executions.
It said the country's "highest leaders" had turned a blind eye to the activities of "death squads" in the North Caucasus for some years. And, it predicted, with the adoption of the new law, those activities would now be seen in other countries too.
The case of Mr Litvinenko has led to an outpouring of conspiracy theories, many of which suggest he was killed by a Russian secret service, of which there are several.
Bulgarian dissident Georgi Markov was assassinated in London in 1978
But in reality, there have been only a very small number of killings by poison of Russia's opponents abroad.
Indeed, the last known case abroad of this type of execution was of Georgi Markov, the Bulgarian dissident assassinated by "poison umbrella" in London in 1978.
Many years later, during the perestroika era, a retired KGB general admitted that he had provided the toxin.
Such events were, however, widespread inside the Soviet Union during the terror of the 1930s to 50s.
The 1958 trial of Pavel Sudoplatov - a lieutenant general in the Soviet secret service, who was closely involved in the execution in Mexico of Trotsky - heard how toxins were "illegally tested" on a large number of prisoners who had been sentenced to death.
In more recent years, there is convincing evidence that an extra-judicial killing was carried out by Russian special forces in Qatar in 2004 when the former Chechen separatist president, Zelimkhan Yandarbiev, was blown up by a car-bomb.