Russia's Foreign Ministry experienced "large-scale" cyber-attacks originating in Iran and Hungary last month, according to spokesperson Maria Zakharova.
On Friday, Zakharova said the attacks on the ministry's mail server, which occurred on June 29, "resulted in grave consequences".
Hackers briefly accessed electronic correspondence between the ministry's staff, Zakharova told reporters during a regular briefing.
The ministry's system administrators temporarily blocked its mail service to stave off the attack, she said.
This is the first time Russia's Foreign ministry has said its servers were successfully hacked.
When a US hacker boasted last October he had successfully hacked the ministry website, Zakharova said he had targeted a defunct version of the sitem The Moscow Times reported.
Zakharova said that 88 per cent of all visits to the site were cyber-atatckers with US IP addresses.
Kremlin spokesman Dmitry Peskov in January revealed its website had been under "hundreds and thousands" of attacks every day from different countries, including China, India and the European Union.