Ukraine's government threatened to block the convoy if the cargo could not be inspected and announced it was organizing its own aid shipment to the war-wracked separatist region of Luhansk.
Later, it also declared it had taken the eastern town of Novosvitlivka, which lies just south of Luhansk, which means it could block the Russian aid convoy from reaching Luhansk.
Taking Novosvitlivka "disrupted the last opportunity for movement between Luhansk and other territories controlled by Russian mercenaries," Ukrainian security council spokesman Andriy Lysenko told reporters.
Lysenko also if the Russians refused to let the Red Cross inspect its cargo "the movement of the convoy will be blocked with all the forces available."
Ukraine suspects the convoy could be a pretext for a Russian military invasion or further support for the pro-Russian rebels it has been fighting since April.
After a clumsy and ineffectual start, Ukraine's forces have taken back much of the territory once held by rebels.
As the circle around the separatists tightens, two of their top figures have resigned in the past week. On Thursday, the rebel Donetsk People's Republic said its defense minister Igor Girkin had resigned.
Both Girkin and former rebel prime minister Alexander Borodai, who was replaced last week, are Russians and both were replaced by Ukrainians. Those moves could indicate an attempt by the separatists to distance themselves from allegations by Kiev and the West that Russia supports or directs the insurgency, charges that Russia denies.
The Russian convoy of more than 200 vehicles had been parked at a military depot in the southern Russian city of Voronezh amid disagreement over how and where the aid could be delivered to eastern Ukraine.
But on Thursday, the white-tarped trucks, some flying the red flag of Moscow and accompanied by military vehicles, drove past sunflower fields and green hills and turned west toward the rebel-held border crossing of Izvaryne.
The trucks pulled off about 28 kilometers (17 miles) from the border with Ukraine and parked in a large field where dozens of beige tents had been set up. Drivers in matching delivery outfits got out and relaxed. It appeared they may be planning to spend the night on Russian soil.
The route suggested Russia was intent on not abiding by a tentative agreement to deliver aid to a government-controlled border checkpoint in the Kharkiv region, where it could more easily be inspected by Ukraine and the Red Cross.
Moscow has insisted it coordinated the dispatch of the goods — which it says range from baby food and canned meat to portable generators and sleeping bags — with the International Committee of the Red Cross.
ICRC spokeswoman Anastasia Isyuk said talks were continuing but she could not confirm where the Russian convoy was headed.
"The plans keep changing, the discussions are going ahead and we will not confirm for sure until we know an agreement has been reached," Isyuk said in Geneva.
Russia says the convoy has 262 vehicles, including about 200 trucks carrying aid.
Russian President Vladimir Putin, meanwhile, addressed hundreds of lawmakers Thursday in the Black Sea resort of Yalta in Crimea, which was annexed by Russia from Ukraine in March. He did not speak specifically about the convoy.
In a relatively subdued address, Putin said Russia's goal was "to stop bloodshed in Ukraine as soon as possible." Moscow should improve life in Ukraine "without building a wall from the West," he said, but asserted that Russia would "not allow anyone to treat us with arrogance."
The Ukrainian government in Kiev countered Putin's aid convoy by announcing one of its own.
Ukrainian Infrastructure Minister Maxim Burbak said three convoys totaling 75 trucks were transporting 800 tons of humanitarian aid from Kiev and the cities of Kharkiv and Dnipropetrovsk — including grain, sugar and canned food. Their eventual destination was Luhansk, he said.
Ukrainian forces have stepped up efforts to dislodge the separatists from their last strongholds in Donetsk and Luhansk and there was more heavy shelling overnight.
The sounds of artillery fire and blasts could be heard all over Donetsk on Thursday. Shells hit two shopping complexes, city authorities said, warning citizens to stay off the streets.
Valentina Smirnova, a resident of Donetsk, cleaned up broken glass and rubble Thursday in her damaged kitchen.
"My son left and now I am staying with my daughter. I don't know what to do afterwards. Where should I run to after that? Please tell me!" she said, tears welling up.
The U.N.'s human rights office in Geneva says the death toll in eastern Ukraine has nearly doubled in the last two weeks — rising to at least 2,086 people as of Aug. 10, up from 1,129 on July 26.
Nataliya Vasilyeva in Yalta, Crimea; Laura Mills in Moscow; Peter Leonard and Jim Heintz in Kiev, Ukraine; and John Heilprin in Geneva contributed to this report.
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