Ukrainian authorities have begun inspecting a Russian convoy carrying what Moscow says is humanitarian aid destined for eastern Ukraine, amid a continuing government offensive against pro-Russian rebels.
The inspections could ease tension over the convoy of some 280 trucks, but reports that Russian military vehicles have crossed into Ukraine reinforced Western concerns about Moscow's motives.
The Ukrainian military said the inspections began in the morning on August 15. Russia says the trucks are carrying water, food, and other aid for people in eastern Ukraine, while Western officials have voiced concern the mission could be a pretext for a military incursion.
Pro-Russian separatists have been fighting Ukrainian forces in the eastern Donetsk and Luhansk regions for months in a conflict that has badly damaged Moscow's ties with the West. Russia denies involvement in the conflict.
Officials say dozens of Ukrainian border guards and customs officers crossed into Russia to inspect the convoy, which halted in the Rostov Oblast town of Kamensk-Shakhtinsky and was joined on August 15 by dozens of Russian armored personnel carriers (APCs).
Reporters for "The Guardian" and "The Telegraph" reported on August 14 seeing about 23 Russian APCs cross into Ukraine, and Lithuanian Foreign Minister Linas Linkevicius said on August 15 that he had reports that 70 pieces of Russian military equipment had crossed into Ukraine overnight.
European Union officials gathering in Brussels for a meeting focusing on Iraq said they were very alamed by the reports. British Foreign Secretary Philip Hammond warned of "very serious consequences" if any Russian military personnel or vehicles in Ukraine were not withdrawn immediately.
Danish Foreign Minister Martin Lidegaard said that both the EU and the United States "have a very strong commitment to respond to any new aggression from Russia."
NATO Secretary-General Anders Fogh Rasmussen, speaking after meeting the Danish defense minister, said a "Russian incursion" had occurred overnight, but stopped short of characterizing it as an invasion.
"It just confirms the fact that we see a continuous flow of weapons and fighters from Russia into eastern Ukraine and it is a clear demonstration of continued Russian involvement in the destabilization of eastern Ukraine," he said.
A regional representative of the Russian border guards service, part of the Federal Security Service (FSB), denied Russian forces had crossed the border.
The representative said rapid-reaction units had been established to travel to areas where shelling or fighting in border areas is reported, but that they operate only on Russian territory.
Russia says humanitarian aid is badly needed in parts of eastern Ukraine affected by fighting that has killed more than 2,000 people in about four months and driven more than 250,000 from their homes.
Authorities in Donetsk, the main separatist stronghold, said 11 civilians were killed in shelling over the previous 24 hours.
The city council said fighting raged overnight in central and western districts of the industrial hub, where authorities said on August 14 that 74 residents had been killed in 72 hours.
The Ukrainian military said fierce fighting had also taken place near Luhansk, closer to the area where the Russian convoy was parked in a field across the border.
"We are at the moment mainly concerned with the humanitarian convoy but actually the next step is about more: It's about what can be done to make the weapons fall silent," German Foreign Minister Frank-Walter Steinmeier said in Brussels.
Ukrainian Foreign Minister Pavlo Klimkin told Bloomberg TV on August 15 that Kyiv was ready for a bilateral cease-fire if several "critical conditions" were met.
He said those conditions included Ukrainian control over the border area, progress on hostages, and the establishment of an Organization for Security and Cooperation for Europe team to monitor the truce, suggesting there would be no decision on a cease-fire soon.
With reporting by Reuters, dpa, AP, ITAR-TASS and Interfax