KIEV, Ukraine (CNN) -- Ukrainian border guards were in Russia on Friday to examine the contents of a huge convoy of trucks that Moscow says is carrying relief goods for civilians in war-torn eastern Ukraine, authorities said.
The Ukrainians' inspection of the trucks -- reflecting Kiev's concerns that Russia might try to smuggle military supplies to pro-Russian rebels -- came as Ukraine's military said it was continuing a major offensive to capture three rebel strongholds.
The battles are an extension of months of fighting that has killed hundreds of people and, aid groups say, left thousands in eastern Ukraine without access to water, electricity and proper medical aid.
At a checkpoint on the Russian side of the border from Ukraine's Luhansk region, 59 Ukrainian border guards and customs officers were inspecting scores of trucks that Russia has said are carrying tons of grain, sugar, baby food, medical supplies and sleeping bags, Ukraine's military said.
The Ukrainian government had expressed fears that the convoy was a large-scale effort to smuggle supplies or troops to pro-Russian rebels -- something it accuses Russia of doing regularly in perhaps smaller deliveries.
But on Friday, Ukrainian military Col. Andriy Lysenko said that the aid is needed and that Ukraine would allow the Red Cross to distribute it if Ukraine and the aid group find the material suitable.
The Red Cross is trying to establish what exactly is in the trucks, Andre Loersch, a Red Cross spokesman in Kiev, said Friday.
"The (Red Cross) will temporarily deploy additional personnel to Ukraine and Russia for the purpose of this operation and is already in the process of identifying its staff ready for deployment," Loersch said. "A four-member team is already present today in the vicinity of the convoy, and more staff are on their way."
Russia has strenuously insisted that it should be permitted to send aid to the conflict-battered region, many of whose residents are Russian speakers. When Russia said this week that it was sending more than 260 trucks of aid to Ukraine, Red Cross officials initially said they didn't know what Russia was talking about, stoking Ukrainian suspicions and international confusion about whether the aid would be let in.
Ukraine: Russian troop carriers sighted
Even as officials inspect the humanitarian aid on the Ukraine-Russia border, Ukrainian officials say Russia still is sending weapons to rebels in Ukraine and building up Russian troops along the border.
A convoy of Russian military vehicles crossed the border overnight, Lysenko said Friday.
The vehicles didn't constitute a Russian invasion of Ukraine, but their sighting represents the latest example of what the Ukrainian government says has been happening for months.
The vehicles and their cargo probably were sent to assist rebels in Luhansk, one of three rebel areas that the Ukrainian military is trying to overrun, Lysenko said.
Battle rages on
Heavy fighting continued in eastern Ukraine on Friday.
Tens of thousands of Ukrainian troops have stepped up efforts to retake areas in and around Luhansk, Donetsk and Horlivka, three cities held by rebels for months.
Donetsk has been the scene of intense shelling for days as rebels try to hold off Ukrainian forces. Eleven civilians were killed in a 24-hour period straddling Thursday and Friday, the Donetsk mayor's office said.
Many districts were without power and water, the mayor's office said. A CNN crew that was in Donetsk earlier noted that the shelling had pushed some residents underground into cellars and half-built basements.
Five Ukrainian troops were killed in the past day, Lysekno said Friday, adding that some rebels were retreating, trying to dig in closer to the Ukraine-Russia border.
The ongoing fighting -- sparked last year with a political crisis over whether Ukraine would seek closer ties with Europe or Russia -- has left more than 2,000 people dead and just under 5,000 wounded in eastern Ukraine since mid-April, according to estimates from U.N. officials.
Hundreds of thousands of people have been forced to flee their homes and seek shelter either elsewhere in Ukraine or across the border in Russia, the United Nations says.
More than 800 people died and more than 1,600 others have been injured in this year's fighting in the Donetsk region alone, the region's health care department said. The department did not give a breakdown of combatants and civilians.
Loersch said the Russian humanitarian convoy was made up of 262 trucks, not 280 as suggested in earlier reports.
Ukrainian and Russian authorities need to agree on the procedure for crossing the border and going through customs, he said.
Russian authorities have shared a general list of items that the convoy is carrying but not a detailed inventory, he said.
The Russian news agency Itar-Tass reported this week that the shipment contains 400 tons of grain, 100 tons of sugar, 62 tons of baby food, 54 tons of medical supplies, sleeping bags and "electrical power units."
The Kiev-recognized governor of Luhansk, Irina Verigina, said Friday that she doesn't want aid from Russia.
"They send us tanks and grads overnight and offer to send humanitarian aid by day," she said.
The United States and the European Union have applied steadily increasing sanctions against Russian officials, banks and other interests since March, when Russia annexed the Black Sea Ukrainian peninsula of Crimea. Russia's move came a month after Ukraine's parliament ousted pro-Moscow President Viktor Yanukovych.
Yanukovych left office after violent protests against his government in the capital, Kiev. Those protests were motivated in part by his decision to back out of a trade deal with the European Union in favor of closer ties with Russia.
-- Journalist Victoria Butenko reported from Kiev, CNN's Jethro Mullen reported and wrote from Hong Kong, and CNN's Jason Hanna reported and wrote from Atlanta. CNN's Radina Gigova, Will Ripley and Lindsay Isaac contributed to this report.
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