Ukraine said on Wednesday it will not recognise Russian passports issued to Ukrainian citizens in the territories occupied by Kremlin-backed rebels, comparing them to Nazi identity documents.
"These passports will be considered illegal," Prime Minister Volodymyr Groysman told the government meeting.
"We will never recognise any citizenship that was issued by the aggressor state. This is like Nazi Germany issuing Ausweis (identity document) for certain people," Groysman added.
Ukrainians with Russian passports will not be able to cross the state border and use them on the territory of Ukraine.
The same rule will apply to Russians who have received their passports at centres that issue documents to residents of separatist republics, warned Groysman.
Kremlin spokesman Dmitry Peskov said Wednesday that Russia "will continue to issue passports to those citizens who want them and who fall under the presidential decree" Vladimir Putin signed in April.
The decree made it easier for people living in eastern Ukraine's separatist territories to obtain Russian passports, drawing swift condemnation from Kiev and its western allies.
Putin also said recently that Ukrainians and Russians were "one people" and would benefit from common citizenship as the "brotherly nations".
The conflict between the Kiev government and breakaway rebels began after Moscow annexed Ukraine's Crimea peninsula in 2014.
The war has claimed some 13,000 lives.