At least some of Russian aid convoy’s 280 trucks are stalled in the Voronezh area, some 300 miles from Moscow after Ukrainian officials said they would not let it in.
Other trucks are said to be heading further south.
There have been fears Russia could use the convoy as a pretext for military action in Ukraine.
The UN says the conflict’s death toll has doubled in the past two weeks.
Altogether, at least 2,086 people have been killed since mid-April, when Ukraine sent troops against pro-Russia rebels in Donetsk and Luhansk regions.
The fighting has displaced almost 300,000 people, many of whom have fled to Russia.
The Russian convoy spent Tuesday night in Voronezh after leaving a military base near Moscow on Tuesday amid fanfare.
A spokesman for President Vladimir Putin said the mission was proceeding in co-operation with the International Committee Red Cross.
The convoy was on the move inside Russia, Dmitry Peskov said, but did not comment on the route.
A Red Cross spokesman told a news conference he did not know the final route for the aid.
“I tried to get information where exactly this convoy is right now before coming here, but I don’t know the exact location still,” said Andre Loersch.
He said the ICRC had received a general description of what is in the trucks. Once it had received a more accurate list, it would be able to start work on how the aid could be transferred and distributed.
Russian TV showed the cargo, including grain, baby food and medicine, bound for civilians trapped by fighting in the area held by pro-Russia rebels.
Ukrainian officials insist that aid should pass through a government-controlled border post and be accompanied by Red Cross officials.
Russian Foreign Minister Sergey Lavrov said on Tuesday that Moscow had agreed to these conditions.
“Provocation by a cynical aggressor is not permissible on our territory,” Ukrainian Interior Minister Arsen Avakov said on his Facebook page.
Ukraine’s PM Arseny Yatsenyuk described the Russian move as “boundless cynicism”.
“First they deliver tanks, Grad [rocket launchers], terrorists and bandits…, and then they deliver water and salt,” Arseny Yatsenyuk said.
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