Uncertainty surrounds the movement and route of a Russian aid convoy bound for east Ukraine after Ukrainian officials said they would not let it in.
At least some of its 280 trucks are stalled in the Voronezh area, some 500km (300 miles) from Moscow. Others 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.
Red Cross co-operation
The convoy spent Tuesday night in Voronezh after leaving a military base near Moscow on Tuesday amid fanfare.
A spokesman for Russian 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 (in Russian).
Prime Minister 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," he said.
War in Ukraine: the human cost
Casualties: At least 2,086 people have been killed in the east since mid-April, including civilians, the military and members of the armed groups, the UN said on 13 August. Nearly 5,000 people have been confirmed wounded. Ukraine said on 11 August that 468 of its soldiers had been killed. The rebels have reported losing at least 800 fighters.
Refugees: Nearly 300,000 people have been forced from their homes this year. More than 117,000 are displaced inside Ukraine, 87% of them from the Donetsk and Luhansk regions, while a further 168,000 have crossed into Russia. Source: UN refugee agency
Nato warned on Monday that the Russians were developing a "narrative and a pretext" for a military operation under the guise of aid.
On Wednesday, UK Foreign Secretary Philip Hammond called on Russia to "state without undue delay the items they intend to supply" and respect the neutrality of the International Committee of the Red Cross (ICRC).
Ukraine has reported in recent days that Russia has massed 45,000 troops on its border.
Advances by Ukrainian troops in recent weeks have put pressure on the rebel-held cities of Donetsk and Luhansk, leaving the latter in particular virtually cut off.
However, reports on Wednesday said that 12 members of the ultranationalist group Right Sector, fighting on the side of the Ukrainian government, had been killed in an ambush near Donetsk. Several others were captured.