LONDON (REUTERS) - Russia's spy chief on Tuesday (May 18) denied responsibility for the SolarWinds cyber attack but said he was "flattered" by the accusations from the United States and Britain that Russian foreign intelligence was behind such a sophisticated hack.

The United States and Britain have blamed Russia's Foreign Intelligence Service (SVR), successor to the foreign spying operations of the KGB, for the hack which compromised nine US federal agencies and hundreds of private sector companies.

"These claims are like a bad detective novel," SVR Director Sergei Naryshkin, a close ally of Kremlin chief Vladimir Putin, told the BBC in Russian.

Asked directly if the SVR was responsible for the SolarWinds attack, Naryshkin quipped with a smile that he would be "flattered" if the SVR had been responsible for such a sophisticated attack but that he could not "claim the creative achievements of others as his own."

Naryshkin said he did not want to accuse the United States of being behind the attack but quoted from documents leaked by former National Security Agency contractor Edward Snowden to suggest that the tactics of the attack were similar to those used by US and British intelligence agencies.

The United States and Britain cast Russia as a dangerous former superpower which they say has poisoned enemies with nerve agents and radioactive isotopes, meddled in Western elections and carried out hacking operations across the world.

Naryshkin said such accusations were absurd and that Russia was not responsible for the cyber-attacks, poisonings, hacks, or meddling in elections that it was blamed for.

The hack of SolarWinds, which was identified in December, gave access to thousands of companies and government offices that used its products.

Microsoft President Brad Smith described the attack as "the largest and most sophisticated attack the world has ever seen."

Britain's GCHQ cyber spying agency said that it was highly likely that SVR was responsible for the SolarWinds attack.