Ukraine accused Russia on Thursday of allowing rebels to bring three tanks and other military vehicles across the border into country’s east to fight the Ukrainian army.
Interior Minister Arseny Avakov stopped short of directly accusing Moscow of sending the tanks – but he made it clear that he held Russian President Vladimir Putin responsible for failing to carry out a promise to tighten controls at the two countries’ border.
The Interfax news agency quoted Avakov as saying that a "column" with armored vehicles crossed from Russia through border posts controlled by pro-Russian rebels near Dyakove village in eastern Ukraine.
Evidence that Russia is sending in weapons or assisting the rebels militarily would further implicate Moscow in the uprising against Kiev's pro-Western leaders, despite Russia’s denials that it has played a role in weeks of fighting.
Avakov said that vehicles including automobiles and armored personnel carriers crossed the border, and that three tanks went to the town of Snizhne about 25 miles from Dyakove. One remained there while two others left in the direction of the town of Horlivka and were engaged by the Ukrainian military, he said, adding that "part of this column has been destroyed" by Ukrainian forces.
Ukraine’s President Petro Poroshenko has discussed the situation with his defense and security chiefs, and then told Putin by phone that the situation was "unacceptable," Poroshenko’s spokesman said.
Moscow did not immediately respond to the accusations, and it was not clear how Putin reacted to Poroshenko by phone.
Russia has already been hit by U.S. and European Union sanctions over events in Ukraine, and could face more. Confirmation of direct Russian involvement in the rebels' uprising would raise the stakes in Moscow's worst standoff with the West since the Cold war ended more than two decades ago.
The separatists, who rose up after Poroshenko's pro-Moscow predecessor was toppled and fled to Russia in February, deny receiving anything but medical supplies, food and clothing from Russia.
"Russia is helping, of course, with humanitarian aid, food, things, medicine, gear. We won't refuse that," a rebel said.
Russia has repeatedly denied providing military support to the rebels who have taken control of several towns and cities in east Ukraine and hope that Russia will annex the region, as it did the Black Sea peninsula of Crimea in March.
Russian Foreign Minister Sergei Lavrov had earlier on Thursday repeated Moscow's view that the onus for ending violence lay with Ukraine, because it has launched a military operation against the rebels.
But he backed Poroshenko's efforts to push through a peace plan that the president has drawn up and discussed with Putin.
"So far, hope remains that President Poroshenko's statements about the end of violence will be implemented," Russia's Interfax news agency quoted Lavrov as saying.