The move appears to signal increasing desperation from Kiev, highlighting it has few options for a real response as opponents take over further territory. A referendum on greater independence from the central government in Kiev has been a key demand made by the militias that have commandeered government buildings in the east.

Russia has also repeatedly called for Ukraine to change its constitution and switch to a federalized system that would grant greater independence to regions, particularly in the east, which are more heavily ethnic Russian and more closely tied to Moscow economically.

“I am certain that a large majority of Ukrainians at this referendum, which, when the parliament decides so, could be held alongside the presidential election, will favor an indivisible, independent, democratic and unified Ukraine,” Ukraine’s acting president, Oleksandr Turchynov, told a meeting of parliamentary leaders. “Any changes to the constitution demand wide discussion in all the regions of Ukraine.” Ukraine is scheduled to hold a presidential election on May 25.