Ukrainian President Petro Poroshenko has called for an emergency meeting of his security chiefs as the two pro-Russian leaders who won the rebel polls were all set to be sworn in the same day.
The meeting will deliberate on a plan to scrap a law that would have offered "special status" to areas in the east including those controlled by the rebels.
The "special status" would have allowed the Donetsk and Luhansk regions to run their own affairs and also offered separatist fighters freedom from prosecution.
The rebel elections, legitimised by Russia's foreign ministry, have been denounced by Kiev and the West, with Poroshenko calling it a gross violation of the Minsk agreement, reports Reuters.
The Minsk agreement, entered into by Ukraine, Russia and the Organization for Security and Co-operation in Europe, provided only for election of local officials under Ukrainian law, and not for separatist ballots that encourage factions close with Russia, insists Kiev.
The polls saw Alexander Zakharchenko, a 38-year-old former mining electrician, and head of the "Donetsk People's Republic", win in Donetsk while another pro-Russian entity saw its leader Igor Plotnisky win in Luhansk.
The elections could further threaten the territorial unity of Ukraine, which lost control of its Crimean peninsula in March when it was annexed by Russia following the overthrow of a Moscow-backed leader.
The White House has also condemned the elections as "illegitimate" and warned of further economic sanctions against Russia if it continued to violate the Minsk deal.
"We are concerned by a Russian Foreign Ministry statement today that seeks to legitimize these sham 'elections,'" Bernadette Meehan, spokeswoman for the White House National Security Council, said in a statement.
Kiev and the West will now be looking to see if Russian President Vladimir Putin will formally validate the election.
All eyes will be on Putin due to appear at a Red Square ceremony in Moscow marking National Unity day.
More than 4,000 people have been killed in the conflict, which saw the US and the European Union slap sanctions against Russia.
The 5 September ceasefire has brought an end to full-scale clashes between government forces and the separatists. After a parliamentary election on 26 October, Poroshenko is now supported by the West determined to stop any further break-up of Ukraine.