Russian troops and armour moved in or around at least three Georgian towns on Thursday, ignoring demands by Washington that Moscow respect Georgia`s territorial integrity.
Reuters witnesses saw Russian troops in the key central Georgian town of Gori and outside the western town of Zugdidi. Residents in the Black Sea port of Poti saw a Russian incursion.
In Moscow, the Russian General Staff said it was legitimate for "Russian peacekeepers" to be in Poti and for what it termed "reconnaissance parties" to be in Gori, two days after Russia signed up to a French-led peace plan to stop the fighting.
Russian armed forces have occupied parts of Georgia since repelling a Georgian attack last week on the tiny pro-Russian separatist territory of South Ossetia.
The conflict has spooked oil markets and alarmed the West, which fears it could spiral out of control.
Sharpening the confrontation with the United States over the future of Georgia, Medvedev received in the Kremlin on Thursday the leaders of the two separatist regions at the heart of the week-old conflict and promised them Moscow`s backing.