Russia has signed friendship treaties with Abkhazia and South Ossetia, sealing diplomatic ties with the breakaway Georgian regions, reported BBC.
The accords include a pledge of military assistance from Russia.
They were signed in the Kremlin by Russian President Dmitry Medvedev and the separatist leaders, in a televised ceremony on Wednesday.
Russian troops ousted Georgian forces from both regions during intense fighting which erupted on 7 August.
The treaties grant Russia the right to build and improve military bases in Abkhazia and South Ossetia, the Itar-Tass news agency reports.
But "the contracting parties shall conclude separate agreements on military co-operation", the treaties said.
Georgia's President Mikhail Saakashvili told the BBC he was "deeply troubled" by the treaties, calling Russia's move "classic invasion and annexation".
Russia plans to keep 3,800 troops in Abkhazia and the same number in South Ossetia.
Russia recognised the independence of the two breakaway regions on 26 August. So far, Nicaragua is the only other country to have done so.
In response to the treaty signings, the US reiterated calls for Russia to respect Georgia's territorial integrity and withdraw its forces to positions occupied before the conflict, in line with an EU-brokered ceasefire deal.
"Our position in support of Georgia's territorial integrity is unchanged," said White House spokesman Gordon Johndroe.
He said the US expected Russia "to live up to the commitments" in the truce agreement.
Mr Medvedev said the new treaties would mean that Russia and the breakaway regions will take "joint necessary measures to eliminate the threat to peace, address problems in this sphere and resist acts of aggression".
"We will show each other all necessary support, including military support," he said, flanked by South Ossetian leader Eduard Kokoity and Abkhaz leader Sergei Bagapsh.
Earlier on Wednesday, Russia condemned a two-day visit to Georgia this week by Nato representatives from all 26 member nations.
During the visit, Nato Secretary-General Jaap de Hoop Scheffer said the door was still open for Georgia to join Nato.
The Russian foreign ministry said a "them and us" mentality was at work, and criticised the Nato ambassadors for checking on damage in Georgia but not in South Ossetia.
It said the Nato chief would have got a more objective picture of the August conflict by visiting Tskhinvali, the heavily war-damaged capital of South Ossetia.
Nato's support for Georgia "can only be seen as encouraging Tbilisi to engage in new reckless adventures," the ministry statement added.
The conflict in the region began on 7 August when Georgia tried to retake South Ossetia by force after a series of lower-level clashes.
Russia launched a counter-attack and the Georgian troops were ejected from both South Ossetia and Abkhazia.
President Saakashvili called for a Nato presence in Georgia, "to make long-term security here and security for Nato". He was speaking in an interview with the BBC's Hardtalk programme.
The signing of the treaties comes a day after the Russian Prime Minister, Vladimir Putin, announced that Russia's defence spending for 2009 would increase by 27%, to the equivalent of almost $95bn (£53bn).