Mikhail Saakashvili addressed world leaders at the UN General Assembly a day after a Nato ministers meeting on the sidelines endorsed stronger ties between the alliance and the former Soviet republic.
Moscow strongly criticised the decision, saying it could upset fragile stability in the Caucasus and hurt Russian interests.
Russian news agencies on Friday quoted Sergei Ivanov, Russia's defence minister, as saying the country would deploy two brigades along the border with Georgia.
Saakashvili told the General Assembly that Moscow was waging a "concerted policy" of distributing Russian passports to residents of the separatist regions of Abkhazia and South Ossetia as part of an alleged plan to take full control of the territories.
He also said that Russian peacekeepers were fostering conflict and anti-Georgian feeling in the regions instead of promoting peace.
Since coming to power three years ago, Saakashvili has pledged to bring Abkhazia and South Ossetia - which broke away from Georgia during wars in the early 1990s - back into the fold. He has accused Russia of supporting separatists in the two provinces and has pushed for the withdrawal of Russian peacekeepers who have been deployed there for more than a decade.
He cited unspecified reports by the UN and the Organisation for Security and Cooperation in Europe (OSCE) to argue that Russian forces "have served to perpetuate rather than resolve the conflicts [and] have abused and made a farce of time-honored principles of neutrality, impartiality and trust".
He told the UN that the Russian mission in Abkhazia had watched more than 2,000 people being killed and more than 8,000 homes destroyed.
He said: "Let us be under no illusion. The residents of our disputed territories are under a form of gangster occupation which hopes the international community will lose interest and reward the results of ethnic cleansing. This cannot be allowed to happen.
"Today, the situation in Georgia is marked both by opportunity and danger. Let us therefore embrace this historical opportunity and not delay."
Sergey Lavrov, the Russian foreign minister, rebuffed Saakashvili's speech as a pack of lies.
"Nothing is further from the truth than this statement. I am amazed by the huge amount of distorted facts in the speech by the Georgian president."