The United States demanded Russia withdraw its equipment and personnel from Ukraine after Moscow sent in a convoy of trucks yesterday in what Kiev called a “direct invasion”.

The White House denounced Russia’s latest move in Ukraine, calling it a flagrant violation of Ukraine's sovereignty and saying Russia should remove it or face more economic sanctions.

Ben Rhodes, the White House deputy national security adviser, told reporters the Russian move adds to the escalation of the Ukraine conflict in a dangerous way.

He said the US planned to discuss the situation with the UN Security Council. He said if the convoy is not removed, the Russians will face “additional costs,” meaning sanctions that have been levied against the Russian economy.

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 de facto charge that Russia was waging war on its former Soviet neighbour.

Moscow, which has thousands of troops close to the Russian side of the border, warned against any attempt to “disrupt” what it said was a purely humanitarian operation; it did not say what action it might take if the Ukrainian military intervened.

The US Pentagon press secretary accused Russia of violating Ukraine’s sovereignty. “Russia must remove its vehicles and its personnel from the territory of Ukraine immediately. Failure to do so will result in additional costs and isolation,” Rear Admiral John Kirby said in Washington.

Ukraine cries ‘invasion’ as convoy passes without Customs or border clearance

The US and EU have already imposed economic sanctions on Moscow and the Kremlin has retaliated; Nato has deployed extra troops in member states bordering Russia, including the Baltic states and Poland.

Ukraine 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. Rasmussen 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 denied breaching international law and the Kremlin said Russian President Vladimir Putin had told German Chancellor Angela Merkel in a telephone call Moscow could no longer wait for Kiev’s green light to help people in distress.

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 somehow 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.”

The fact Russian vehicles had crossed into Ukraine without permission “testifies to the deliberate and aggressive character of actions by the Russian side”, it said.

A Reuters witness said the white-painted trucks had crossed on to 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 EU 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.

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