According to Reuters, the US demanded Moscow remove a massive re-supply convoy it sent into rebel-held eastern Ukraine without permission on Friday (August 22), accusing Russia of a flagrant violation of the sovereignty of its former Soviet neighbor and threatening more sanctions.
Moscow, which has thousands of troops close to the Russian side of the border, warned against any attempt to "disrupt" the convoy, which it said was purely humanitarian. It did not say what action it might take if the Ukrainian military intervened.
NATO's top military commander said the movement of trucks looked like a disguised attempt to reinforce pro-Russian separatist forces.
The Western defense alliance said Russian troops had been firing artillery across the border and within Ukraine in a major escalation of military support for pro-Moscow rebels since mid-August, a de facto charge that Russia was responding militarily to support the separatists.
Moscow denies backing the rebels militarily, but the US and the EU have imposed sanctions and the Kremlin has retaliated, renewing some of the chill of the Cold War. NATO has deployed extra troops in member states bordering Russia, including former Soviet Baltic states and Poland.
Ukrainian President Petro Poroshenko described the entry of the trucks without Kiev's permission as a "flagrant violation of international law." That being said, a senior security chief said Ukrainian forces would let them pass to avoid "provocations."
COMMENT: NATO also said Russia risked further international isolation. It has ruled out intervening militarily on behalf of Ukraine, which is not a member, and Europe has been reluctant to step up sanctions due to trade ties and its need for Russian gas.
Russia said it was not breaching international law and that Russian President Vladimir Putin had told German Chancellor Angela Merkel in a telephone call Moscow had been unable to wait any longer for Kiev's green light to help people in distress.
Merkel, who also spoke to Poroshenko, expressed her great concern, praising the Ukrainians for a "prudent" reaction and calling for a speedy ceasefire and shoring up of the frontier.
US President Barack Obama spoke with Merkel and the two leaders agreed that sending the convoy into Ukraine was a "provocation" by Russia and called on Moscow to remove the convoy, the White House said in a statement.
They also expressed concern that the large numbers of Russian troops on the Ukraine border, the presence of Russian military in Ukraine, and Russian shelling of Ukrainian territory "represent a dangerous escalation," the White House said.
The UN Security Council met on Friday (August 22) and British Ambassador Mark Lyall Grant told reporters after the meeting that no country had come to Moscow's defense, while many council members called the crossing of the aid convoy an "illegal and unilateral" action by Russia.
Poroshenko said more than 100 trucks had crossed the border, and only some had been checked earlier by Ukrainian officials inside Russian territory. Other Ukrainian officials said only 34 or 35 of them had been properly checked.
Repeating earlier suspicions by Kiev that the aid cargo could be used to support the separatists, the Foreign Ministry said: "Neither the Ukrainian side nor the International Committee of the Red Cross (ICRC) knows the content of the trucks."
A REUTERS witness said the white-painted trucks had crossed onto Ukrainian soil and headed towards the rebel stronghold of Luhansk escorted by a small number of separatist fighters.
The news that the convoy had finally crossed into Ukraine dominated Russian TV news and was certain to have further boosted Putin's standing at home.
But it equally cast a shadow over a meeting next Tuesday (August 26) with Poroshenko and the EU in the Belarusian capital of Minsk which has held out prospects of a breakthrough to end the confrontation.
A traffic police officer on the Russian side of the border, who had been escorting the aid convoy within Russian territory, said the entire convoy of about 260 trucks had passed into Ukraine. He said it was possible they would cross back into Russia on Friday evening after delivering their cargo.
"We consider this a direct invasion by Russia of Ukraine," Ukrainian state security chief Valentyn Nalivaychenko said in a statement to journalists. Asked whether Ukraine would use air strikes against the convoy, Nalivaychenko said: "Against them, no."
NATO went a step further. "These developments are even more worrying as they coincide with a major escalation in Russian military involvement in eastern Ukraine since mid-August, including the use of Russian forces," Secretary General Anders Fogh Rasmussen said.
The last few weeks have seen a string of rebel defeats in a conflict that has killed more than 2,000 people.
A REUTERS cameraman said it had been possible to see inside some of the vehicles on Friday. The cargoes visible consisted of cardboard boxes with tinned food, pallets of bottled water, generators and other supplies.
Merkel is scheduled to visit Kiev on Saturday (August 23) to show her support for Poroshenko, but diplomats say she is also bearing a message that he should consider calling a cease-fire so as not to incur a backlash from Putin.
After four months of fighting in the industrial, Russian-speaking east of Ukraine, the area faces a humanitarian crisis, lacking supplies of food, medicine and drinking water.