"We will definitely consider response measures, which is what diplomacy calls for", Grushko told reporters.
Bulgaria said earlier that Russia had been asked to recall a diplomat after he was accused of espionage. The diplomat has reportedly left the country.
According to the Focus news agency, the Bulgarian Foreign Ministry has demanded that Russia recall the diplomat following a statement by the country's prosecutor general saying that his office is terminating an investigation against a Russian citizen suspected of working for Russian intelligence services because of his diplomatic status.
Bulgarian prosecutors have recently charged Nikolay Malinov, chairman of the National Russophile Movement in Bulgaria, with spying for certain Russian institutions and organisations, including the Russian Institute for Strategic Studies, and of laundering money sent by them.