Russia's former president Dmitry Medvedev says Moscow could formally annex two breakaway regions of neighbouring Georgia.
Abkhazia and South Ossetia have effectively been under the control of Moscow since a short conflict between Russia and Georgia over the regions in 2008.
Moscow recognises both as independent states, while most United Nations members view them as Russian-occupied Georgian territory.
Mr Medvedev, who was president in 2008 when Moscow formerly recognised the two regions as independent, has now suggested they could formally join Russia.
In an article published by Russian newspaper Argumenty i Fakty on Wednesday - the 15th anniversary of Mr Medvedev's decree - he wrote: "The idea of joining Russia is still popular in Abkhazia and South Ossetia.
"It could quite possibly be implemented if there are good reasons for that."
He suggested such a move could be pushed forward if Georgia takes steps towards joining NATO.
"We will not wait if our concerns become closer to reality," Mr Medvedev wrote.
Both Abkhazia and South Ossetia held autonomous status within Georgia during its period under the control of the Soviets.
When Georgia declared independence from the Soviet Union in 1991, both regions declared their own intention to break away.
This led to armed conflicts between the separatists and the newly-formed Georgian government, who attempted to take control of the regions by force.
Moscow decided to support the breakaway regions, aggravating relations between Georgia and the post-Soviet Russian government.
The tensions came to a head in 2008, when the Georgian armed forces launched an offensive to take control of Abkhazia, sparking a short war between Russia and Georgia.
Russian troops entered both Abkhazia and South Ossetia and pushed back the Georgian forces, before Mr Medvedev signed a decree formally recognising the two regions as independent states.
Georgia responded by declaring the move an annexation of its territory.
The vast majority of United Nations members also refused to recognise the independence of the two breakaway regions.
Since then, Georgia has maintained mixed diplomatic relations with its far-bigger neighbour.
Tbilisi criticised Russia's 2014 annexation of Crimea and its 2022 invasion of Ukraine, from which Moscow annexed four more regions in September last year.
However, Georgia, which relies on Russia for tourism and the exportation of its wine, has not joined the West in imposing sanctions on Russia.
Moscow, meanwhile, has strongly opposed suggestions that Georgia could one day join NATO.
Georgian officials have repeatedly expressed a desire to join the military alliance, on the basis that it would help to secure the country's territorial integrity.