The European Union condemned Moscow on Thursday for making it easier for people in separatist areas of east Ukraine to obtain Russian passports, calling it a fresh assault on the war-torn country's sovereignty.
The controversial decree signed by President Vladimir Putin "is another attack on Ukraine's sovereignty by Russia", a spokeswoman for EU foreign affairs chief Federica Mogherini said in a statement.
"The timing of such a decision immediately after Ukraine's presidential election... shows Russia's intention to further destabilise Ukraine and to exacerbate the conflict," the spokeswoman added.
The EU urged Russia "to refrain from actions that are against the Minsk agreements and impede the full reintegration of the non-government controlled areas into Ukraine".
Germany and France on Thursday also condemned Moscow, saying the move undermined the Minsk peace agreements.
That deal was signed by the leaders of Russia, Ukraine, France and Germany in the Belarus capital of Minsk in 2015.
Putin's decree was signed three days after Ukraine elected a new president and is aimed at residents of the unrecognised Donetsk and Lugansk republics that broke away from Kiev in 2014 and are governed by Moscow-backed rebels.
People living in the separatist regions will now be entitled to receive a Russian passport within three months of applying.
Ukraine's president-elect Volodymyr Zelensky, a comedian who won Kiev's weekend vote, has called for more international sanctions against Russia in response to the move.
Lithuania on Thursday also condemned Russia's actions and called for the tightening of sanctions.
The foreign minister "strongly condemns the decree signed by Russian President Vladimir Putin," said a government statement.
The conflict between the Ukrainian government and breakaway rebels began after Moscow annexed Kiev's Crimea peninsula in 2014.
The war has claimed some 13,000 lives despite repeated efforts, led by France and Germany, to broker a lasting ceasefire.