KAMENSK-SHAKHTINSKY, Russia -- A Russian aid convoy of more than 200 trucks pushed up to the border with Ukraine on Thursday but then stopped, poised to cross into rebel-held territory.

The Ukrainian government threatened to use all means available to block the convoy if the Red Cross was not allowed to inspect the cargo. Such an inspection would ease concerns that Russia was using the shipment as cover for a military incursion in support of the separatists, who have come under growing pressure from government troops.

Ukraine also announced it was organizing its own aid shipment to the war-racked separatist region of Luhansk.

Complicating the dispute over the dueling missions, Ukraine said Thursday that it had gained control over a key town near Luhansk, thereby giving it the means to block the presumed route that the Russian convoy would take to the city. The town, Novosvitlivka, lies about 25 miles from the border.

The Russian convoy set out Thursday morning from a military depot in the southern Russian city of Voronezh where it had been parked since late Tuesday. Moscow said the convoy has 262 vehicles, including about 200 trucks carrying aid.

The white-tarped trucks, some flying the red flag of Moscow and escorted by military vehicles, stopped about 17 miles from the border and parked in a large field where dozens of beige tents had been set up.

Russia had made a tentative agreement to deliver aid to a Ukrainian government-controlled border checkpoint in the Kharkiv region, where it could more easily be inspected by Ukraine and the Red Cross.

Taking the town of Novosvitlivka "disrupted the last opportunity for movement between Luhansk and other territories controlled by Russian mercenaries," Ukrainian security council spokesman Andriy Lysenko said.

Lysenko also said that 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 that the convoy could be a pretext for a Russian military invasion or further support for the pro-Russia rebels Ukraine 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.

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 to counter allegations by Kiev and the West that Russia supports or directs the insurgency, claims that Russia denies.

The Russian convoy had been parked at the military depot in Voronezh because of the disagreement over how and where the aid could be delivered to eastern Ukraine.

Moscow has insisted it coordinated the dispatch of the goods -- which it says include baby food, canned meat, portable generators and sleeping bags -- with the International Committee of the Red Cross.

Red Cross spokesman 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.

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 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 -- including grain, sugar and canned food -- from Kiev and the cities of Kharkiv and Dnipropetrovsk. 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 U.N.'s human-rights office in Geneva says the death toll in eastern Ukraine has nearly doubled in the past two weeks -- rising to at least 2,086 as of Sunday, up from 1,129 on July 26.

Information for this article was contributed by Nataliya Vasilyeva, Laura Mills, Peter Leonard, Jim Heintz and John Heilprin of The Associated Press.

A Section on 08/15/2014