IZVARINO BORDER CROSSING, Russia - T he United States demanded Moscow remove an aid convoy it sent into rebel-held eastern Ukraine without permission on Friday, accusing Russia of a flagrant violation of the sovereignty of its former Soviet neighbour 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 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 defacto charge that Russia was already waging war.
White House deputy national security adviser Ben Rhodes said Washington planned to discuss the situation with the UN Security Council on Friday and that if the convoy was not pulled out, the Russians would face "additional costs".
Moscow denies backing the rebels militarily but the United States and European Union 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 ex-communist Poland.
Ukrainian President Petro Poroshenko described the entry of the trucks without Kiev's permission as a "flagrant violation of international law". But a senior security chief said Ukrainian forces would let them pass to avoid "provocations".
Kiev called on international allies to unite in "a decisive condemnation of illegal and aggressive actions" by Russia.
NATO also said Russia risked further international isolation, although Europe has been reluctant to step up sanctions due to trade ties and its use of 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.
Poroshenko said more than 100 trucks had crossed the border, of which 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 knows the content of the trucks. This arouses special concern." 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 presence of the Russian trucks could force Ukrainian troops encircling Luhansk to rein in their offensive against the rebels there, because if they hit one of the Russian vehicles, that could give Moscow justification for a full-scale invasion.
Any lull in fighting that resulted would give a badly-needed respite to the rebels in Luhansk, who have been facing defeat, and allow them to regroup.
The news that the convoy had finally crossed into Ukraine dominated Russian TV news channels and was certain to have further boosted Putin's standing at home.
But it equally cast a shadow over a meeting next Tuesday with Poroshenko and the European Union in the Belarussian capital of Minsk which has held out prospects of a breakthrough to end the confrontation.
Mikhail Denikin, chairman of the village council in Izvaryne, on the Ukrainian side of the border, stood by the road waving a large Russian flag as the trucks drove past. "Big thanks to Russia. Our brothers did not forget us. We are brothers. That is the most important thing. We are Slavs, we are together," Denikin told Reuters Television.
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." But Ukrainian authorities said the convoy would pass through an area where the rebels were firing so its security could not be guaranteed. Interfax news agency said later that the first trucks had reached rebel-held Luhansk.