Russia has denied any involvement in cyber attacks on Yahoo after the US claimed it had arrested two FSB agents for cracking 500 million user accounts of the technology company.
"As we have said repeatedly, there can be absolutely no question of any official involvement by any Russian agency, including the FSB, in any illegal actions in cyberspace," Kremlin spokesman Dmitry Peskov told media on Thursday.
The US Justice Department said on Wednesday it had arrested the two senior Russian cyber security officials and a pair of hackers for illegally accessing information from Yahoo, Google, and other webmail providers.
The attacks, the US said, began in 2014 with the apparent twin goals of spying for the government and personal gain.
Peskov said Russian officials found out about the arrests from media sources and were not informed through official channels but the Kremlin was ready to help out US authorities in the case.
"Russia has always expressed interest … in cooperation in the field of countering cyber-crime and ensuring cyber-security. We believe that this is one of the priorities in our time,” he said.
It was the first time Washington had filed criminal charges against Russian agents over cyber-related offenses.
A separate investigation is underway into alleged cyber-meddling by Russian agents in the US presidential election.
Identity of alleged agents
The arrested agents implicated in the cyber-case were identified as Dmitry Dokuchaev,33, and Igor Sushchin,43, both intelligent officers in the FSB, the successor agency to Russia's KGB.
The US said Dokuchaev was an officer in the FSB's Center for Information Security, known as Center 18, which is tasked with investigating hacking and is the US Federal Bureau of Investigation (FBI) point of contact in Moscow for cyber-crimes.
Dokuchaev was reported last year to have been arrested in Moscow by Russian authorities on treason charges linked to the US. He is accused of directing the Yahoo hacking along with a superior officer.
The FSB officers "directed, facilitated and paid criminal hackers to collect information through computer intrusions," acting US assistant attorney-general Mary McCord told reporters.