Q: (Niall) Was Rasputin's assassination the work of a foreign intelligence operation?
A: No.
(Ze Germanz) Who killed Rasputin and why?
A: The equivalent of Mossad for those times.
Q: (L) And why?
A: Too much influence on royal family plus the ability to foresee danger.
If it wasn't a foreign intelligence then it could have been the Russian secret police Okhrana. From Wiki:
Formed to combat political terrorism and left-wing revolutionary activity,[2] the Okhrana operated offices throughout the Russian Empire, as well as satellite agencies in a number of foreign countries. It concentrated on monitoring the activities of Russian revolutionaries abroad, including in Paris...
The Okhrana deployed multiple methods, including covert operations, undercover agents, and "perlustration"—the reading of private correspondence. The Okhrana's Foreign Agency also served to monitor revolutionary activity.[3] The Okhrana became notorious for its agents provocateurs...
Many historians, such as the German historian Konrad Heiden[6] and the Russian historian Mikhail Lepekhine[7] maintain that Matvei Golovinski, a writer and Okhrana agent, fabricated the first edition of The Protocols of the Elders of Zion (1903).
Despite the reforms[9] in the early 19th century, the practice of torture was never truly abolished.[10] Possibly, the formation of the Okhrana led to increasing use of torture,[11] due to the Okhrana using methods such as arbitrary arrest, detention and torture to gain information.[12] Claims persisted the Okhrana had operated torture chambers in places like Warsaw, Riga, Odessa and in a majority of the urban centres.[13]
Just as the Okhrana had once sponsored trade unions to divert activist energy from political causes, so too did the secret police attempt to promote the Bolshevik party, as the Bolsheviks seemed a relatively harmless alternative to more violent revolutionary groups.
And it seems that Rasputin was under surveillance by Okhrana.