Russian border guards have begun patrolling the de-facto borders of Georgia’s rebel regions of South Ossetia and Abkhazia – a move described by Tbilisi as provocative.
It is part of a joint protection agreement between Moscow and two former Georgian republics.
Both regions were recognised by Moscow as independent states after a brief war between Russia and Georgia last year.
At the signing ceremony, the Russian President took the opportunity to criticise NATO for planning to hold military exercises in Georgia next week.
Dmitry Medvedev said there should not be exercises where a war has been fought and that it amounted to a challenge from the West.
He also added the operation could have negative consequences for those who made the decision to hold them.
19 NATO countries and 1,300 troops are expected to take part in the training exercise, although Serbia, Moldova and Kazakhstan have withdrawn.