A Ukrainian security spokesman has said that a humanitarian convoy being dispatched to eastern Ukraine by Russia will not be admitted into the country.
Andriy Lysenko, a spokesman for Ukraine's National Security and Defence Council, said the convoy had not been certified by the International Committee of the Red Cross.
A convoy of 280 Russian trucks headed for Ukraine early on Tuesday, one day after agreement was reached on an international humanitarian relief mission.
But the Red Cross, which was due to coordinate the operation, said it had no information on what the trucks were carrying or where they were going. That has raised fears in Ukraine and the west, where leaders have voiced concerns thatRussia could use the initiative as a pretext for sending troops into separatist-held territory.
An aide to the Ukrainian president, Petro Poroshenko, said Kiev would require the aid to be reloaded onto other transport vehicles at the border by the Red Cross if it was to enter. "We will not allow any escort by the emergencies ministry of Russia or by the military. Everything will be under the control of the Ukrainian side," the aide, Valery Chaly, said.
Earlier on Tuesday, the Itar Tass news agency had said the convoy departed from near Moscow, meaning it would take it a couple of days to arrive in east Ukraine, about 620 miles to the south-west. "It has all been agreed with Ukraine," Business FM radio quoted President Vladimir Putin's spokesman, Dmitry Peskov, as saying.
Thousands of people are said to be short of water, electricity and medical aid due to the fighting. The US president, Barack Obama, has said any Russian intervention without Kiev's consent would be unacceptable and violate international law.
The European commission president, Jose Manuel Barroso, warned on Monday "against any unilateral military actions in Ukraine, under any pretext, including humanitarian".
Russian state television Rossiya 24 showed several heavy white trucks departing from the town of Alabino near Moscow. A correspondent at the scene said the convoy should arrive at the Ukrainian border in two to three days where it would meet representatives of the International Committee of the Red Cross (ICRC).
Russia has said the aid would be delivered together with the ICRC.
The ICRC said on Monday that it had submitted a document to Russian and Ukrainian officials. However the independent agency said it needed agreement from all parties as well as security guarantees to carry out the operation, as it does not use armed escorts.
"The practical details of this operation need to be clarified before this initiative can move forward," said Laurent Corbaz, head of ICRC operations for Europe and central Asia.
According to UN agencies more than 1,100 people have been killed including government forces, rebels and civilians in the four months since the separatists seized territory in the east and Kiev launched its crackdown