The parliament of Georgia's breakaway Abkhazia region has voted to recognise the opposition candidate as the victor in disputed presidential elections.
Bagapsh says he will be inaugurated on 6 December
Sergey Bagapsh is thought to have defeated his rival Raul Khadzhimba, backed by Russian President Vladimir Putin, in the October election.
The MPs' decision came in defiance of outgoing president Vladislav Ardzinba, who has called for a repeat election.
Uncertainty over the results has kept the situation extremely volatile.
The Supreme Court originally declared Mr Bagapsh the winner of the 3 October poll but later annulled the ruling.
Mr Bagapsh has vowed to hold his inauguration ceremony on 6 December whether or not the current leadership considers it legitimate.
But Mr Khadzhimba, quoted by Russia's Itar-Tass news agency, said the
parliament resolution was "an absurd decision, which will deepen
the split in the society".
Mr Ardzinba earlier this week said he would not leave office until a president was chosen in new elections.
The events in Abkhazia are being closely watched by the Georgian authorities, who consider re-establishing control in Abkhazia their key priority.
Abkhazia has been de facto independent since a bloody inter-ethnic conflict in the early 1990s.
Russia has repeatedly stated that it respects Georgia's territorial integrity, but Abkhazia, where most residents hold Russian passports, is often referred to as Russian protectorate.