Russian state media say a convoy of 280 trucks carrying humanitarian aid has left for war-torn eastern Ukraine.
Russian television reported Tuesday the aid mission is being carried out in cooperation with the International Committee of the Red Cross.
But the relief agency, in a statement Monday, said no agreement on Russian participation is in place and said "practical details need to be clarified" before such a mission could move forward.
Thousands of people in Ukraine's Russian-speaking east are reported short of water, medical aid and electricity, as Ukraine forces battle pro-Russian separatists trying to establish an autonomous region near the Russian border.
Russia's announcement of a relief mission has triggered cautious statements from Western governments, warning Moscow not to use humanitarian aid as a pretext for a military invasion.
Earlier Monday, President Barack Obama and his Ukraine counterpart Petro Poroshenko spoke by phone and agreed that any Russian presence in Ukraine without Kyiv's consent would violate international law.
Ukraine's presidential website later said a blueprint for the relief mission calls for participation by the European Union, Russia, Germany and "other partners."
Meanwhile, a Ukrainian military spokesman said Monday that government forces were preparing the "final stage" of retaking Donetsk, the main stronghold of the pro-Russian separatists in eastern Ukraine.
Andriy Lysenko told Reuters that government forces had already cut Donetsk off from neighboring Luhansk, but would move to retake Donetsk first because, in his words, "it is more important."
Lysenko warned civilians in Donetsk and Luhansk to leave the areas "temporarily" to avoid the coming assault.