"The Russian side expressed a resolute protest and flatly demanded that Lt. Col. Boiko be immediately released," the ministry said in a statement. "Otherwise, all responsibility for the consequences would rest with the Georgian side."
The ministry said Moscow regarded this "unprecedented" move as "another planned provocation to discredit Russian peacekeepers, aggravate the situation in South Ossetia and further deteriorate Russian-Georgian relations."
The Georgian ambassador said Russia's demarche would be thoroughly studied in Tbilisi, the ministry added.
Russian military observer Lt. Col. Roman Boiko was detained by Georgia's State Security Department in the city of Gori on October 21. He was placed in a detention center in Tbilisi, the capital of Georgia.
A representative of the Russian embassy in Georgia was allowed to visit the detained observer in the detention center.