The convoy was expected to arrive at a border checkpoint in Kharkiv, where arrangements had been made for the International Committee of the Red Cross to examine and receive the contents before distribution to embattled Luhansk.
Ukraine's National Security and Defense Council spokesman, Andriy Lysenko, said Wednesday that the convoy did not arrive at the checkpoint as planned, and that its final route is unknown.
"Indeed, there is information that the convoy does not reach the limits of Ukraine in Kharkiv region, but it is not known where it will go further."
The delivery of Russian aid has been met with concern and skepticism because it was dispatched without the necessary approvals from the Ukrainian government or coordination with the Red Cross, which is overseeing international humanitarian relief efforts.
On Tuesday, the Red Cross said that it had not yet received "important details" regarding the Russian convoy of humanitarian aid, including content and volume.
There is concern that the convoy could be a pretext for Russia to further agitate the conflict and destabilize Ukraine.
Sviatoslav Tseholko, press secretary to Ukrainian President Petro Poroshenko, said Wednesday that Russia had rejected the proposal of the Red Cross to receive and process the aid and remarked that in doing so, Russia could be pursuing one of three scenarios:
"First. Direct invasion of the territory of Ukraine under the pretext of humanitarian cargo.
"Second. Provocations with the load in Kharkiv region with a high probability of aggression by Russia.
"Third. Help Luhansk by passing through the checkpoint closest to this Ukrainian city. Our customs officers, border guards and the OSCE can scan the goods on the Russian-Ukrainian border. The mission will move to a territory that is under the control of the militants. After arrival in Luhansk, the Red Cross will distribute the aid among the civilians."
Ukrainian officials reiterated Wednesday that any Russian aid deliveries would not be allowed to cross into Ukraine. Instead, both the Ukrainian branch of the Red Cross and personnel from Geneva would accept deliveries of aid at the border, process the aid through customs checkpoints and re-load the supplies onto other vehicles.
If any convoys from Russia -- or any other country -- attempt to cross into Ukraine without proper approvals, they will be viewed as a threat, the NSDC warned.
"Any convoys that are accompanied by the military or consist of the military, and do not have a mandate of the Red Cross and are not a humanitarian aid under its auspices, are viewed as aggressive forces, respectively, the reaction to it will be adequate."