Russia has signed a peace plan for ending a nine-day conflict with Georgia.
But Foreign Minister Sergei Lavrov said the withdrawal of Russian forces from deep inside Georgia depended on extra security measures being put in place.
The truce was brokered by France.
He said Russian forces were encountering "problems caused by Georgia", and refused to put a timetable on their departure.
The conflict between Georgia and Russia erupted on 7 August when Georgia launched an assault to retake the Russian-backed separatist province of South Ossetia.
It led to a massive counter-offensive by Russia, with Russian forces moving deep into Georgian territory.
Scores of people have been killed by the fighting and thousands displaced.
Georgia has vowed it will not accept any loss of its territory, but Russia says the residents are unlikely to want to live in the same state as Georgians.
The future of another breakaway region, Abkhazia, is also at stake.
Georgian President Mikhail Saakashvili signed the truce on Friday. Russian President Dmitry Medvedev followed suit on Saturday.
Among the six points in the agreement, both sides agree to pull back their forces to pre-conflict positions.
But reports say the agreement contains a provision that allows Russia to implement additional security measures on a temporary basis before the arrival of international ceasefire monitors.
Russian forces are now far beyond South Ossetia's borders in Georgian territory. They are reported to be within 35km of the capital, Tbilisi.
Russia argues they are there to ensure civilians face no threat from Georgian troops.
South Ossetia has had de facto independence since the end of a civil war in 1992.