A Russian aid convoy of nearly 300 trucks is nearing the Ukraine border, despite warnings from Kyiv the convoy may not be allowed in.
Prime Minister Arseniy Yatsenyuk on August 13 denounced Russia's "cynicism" and said Ukraine will accept humanitarian aid only from the International Committee of the Red Cross (ICRC).
Interior Minister Arsen Avakov wrote on Facebook: "No convoy of Putin's will be let through Kharkiv region. A provocation by the cynical aggressor on our territory is unacceptable."
Russia says the route of the convoy has been agreed with Kyiv and that once it crosses the border, it will continue under ICRC supervision.
The ICRC has said it would deliver the aid if its principles of neutrality and impartiality are respected. It also says it still needs information on the convoy.
ICRC spokeswoman Anastasia Isyuk said there were still "a number of important issues that need to be clarified between the two sides, including border crossing procedures, customs clearance and other issues."
Isyuk said the ICRC also needs a detailed inventory of the goods the convoy is bringing and so far Russia has provided only a "general list" of the humanitarian aid heading toward Ukraine.
Ukrainian and Western officials have voiced concerns that Russia could use the pretext of humanitarian aid to send troops into eastern Ukraine, where government forces are fighting pro-Russian separatists.
Moscow denies it is supplying the separatists with weapons and expertise.
On August 12, Ukraine said the aid could be delivered through a government-controlled border post and be accompanied by ICRC officials.
Russian Foreign Minister Sergei Lavrov also said on August 12 that Moscow had agreed the route of the convoy with Kyiv and that the trucks will be accompanied by ICRC and OSCE officials, as well as "representatives of the Ukrainian authorities."
Russia says it is sending some 2,000 tons of aid consisting of power generators, grain, canned meat and dairy products, water, baby food, medical supplies, and other items.
The aid is destined for the separatist-controlled city of Luhansk, where thousands of civilians have been without electricity and water for days.
Luhansk and Donetsk are the only two big remaining strongholds of the rebels, who have lost ground to government forces in recent fighting.