Ethnic Armenian separatists in Nagorno-Karabakh agreed to dissolve their government by the end of the year and become a full part of Azerbaijan in the wake of Baku's lightning offensive.

The dramatic announcement on Thursday came moments after it became clear that more than half of the rebel region's population had fled the advancing Azerbaijani forces.

It drew the curtain on one of the world's longest and seemingly most irreconcilable "frozen conflicts" — one that successive administrations in Washington and leaders across Europe had failed to resolve in ceaseless rounds of talks.