Ukraine's interim President Olexander Turchynov says he has ordered the withdrawal of armed forces from Crimea.
The decision was taken because of Russian threats to the lives of military staff and their families, the president announced.
Russian troops have seized most of Ukraine's bases in the peninsula, including the naval base at Feodosia.
Earlier this month, Russia annexed Crimea after a referendum which Ukraine and the West considered illegal.
The G7 group of industrialised countries is to consider a collective response to the crisis during talks in The Hague.
G7 leaders are meeting on the sidelines of a long-planned summit on global threats to nuclear security.
"The national security and defence council has reached a decision, under instructions from the defence ministry, to conduct a redeployment of military units stationed in the Autonomous Republic of Crimea," interim President Turchynov said.
The soldiers' families were also to be evacuated, he added.
The announcement came shortly after Russian troops captured the naval base at Feodosia, the third such takeover in 48 hours.
Defence spokesman Vladislav Seleznyov said the Russians had attacked the base from two directions using armoured personnel carriers and stun grenades.
Feodosia was one of the last remaining bases under Kiev's control, but had been surrounded by Russian forces for some time, the BBC's Mark Lowen in Crimea said.
Two other military bases were stormed and seized on Friday.
Moscow's annexation of Crimea came after protesters overthrew pro-Kremlin President Viktor Yanukovych in February.
Russia said it had acted to protect its "compatriots" in Crimea from "fascists" moving in from mainland Ukraine.
The US and EU have responded with a series of sanctions targeting those individuals including senior officials whom they accuse of involvement in Crimea's annexation.