West fears 280-truck operation is a prelude to invasion while Moscow insists it wants to help residents trapped by conflict

A Russian convoy allegedly carrying humanitarian aid to eastern Ukraine appeared to be in western Russia on Wednesday night after the Kiev government said it would not permit the supplies to enter its territory.

The 280 military trucks hastily repainted white by Russian soldiers had been expected to reach the Ukrainian border near Kharkiv on Wednesday afternoon, but after the Ukrainian prime minister, Arseniy Yatsenyuk, said the country would only accept humanitarian aid from the Red Cross an emergencies ministry camp set up to receive the convoy was dismantled.

Photographs taken on Wednesday suggested the convoy was still in western Russia. It had spent Tuesday night in Voronezh, and in fact may have never left. An Associated Press reporter tweeted a photo on Wednesday afternoon of a white truck he said was from the convoy near a Voronezh military base.

Another location was claimed by a Russian journalist travelling with the convoy who tweeted a photograph of a Russian city he said had been taken from a "hill in the Rostov region," farther to the south. The border crossings still controlled by pro-Russian rebels lie between Luhansk, which is the place most in need of humanitarian aid, and the Rostov region.

If the convoy entered Ukraine there, it would likely further inflame tensions between Moscow and Kiev. The west fears the operation may be a prelude to a Russian invasion, but Moscow insists it is designed to relieve the suffering of besieged residents trapped by conflict.

Vladimir Putin's spokesman Dmitry Peskov told reporters on Wednesday night that the convoy was continuing to move through Russia but he didn't provide a more exact location.

Viktoria Zotikova, a representative of the International Committee of the Red Cross in Moscow said it did not have any information on the whereabouts of the convoy and did not know when or where it would possibly cross the Ukrainian border.

The convoy of 280 Russian trucks head for south-eastern Ukraine early on Tuesday Photograph: AP

"We are willing to take over the assistance from Russia and be in charge of the convoy, but we can't without the Ukrainian authorities," Zotikova said. "What's important is that they decide how it will cross, how it will go further, how the supplies will be stored. We would have to know for sure that the Ukrainian side has checked the cargo and agreed on the contents of it."

Ukrainian president Petro Poroshenko's spokesman said Russia had rejected an offer for the aid to be reloaded onto a Red Cross convoy. He said another possibility would be for the convoy to enter Ukraine through a government-controlled border crossing in the Luhansk region and have its contents checked by border guards, after which it would travel to the regional capital, where Red Cross representatives would distribute the aid.

The latest developments came after Russia's foreign minister, Sergei Lavrov, had claimed on Tuesday that a deal had been agreed with the Ukrainian side, which would allow the convoy to drive into Ukraine. Lavrov claimed an earlier plan to offload the cargo and transport it on Ukrainian trucks had been abandoned on the grounds of cost.

The prospect of Russian intervention in eastern Ukraine – the scene of fierce fighting between Ukrainian troops and Russian-backed separatists – has alarmed the US and EU.

On Monday, the Nato secretary general, Anders Fogh Rasmussen, said there was a "high probability" of a Russian attack which might happen "under the guise of a humanitarian operation".

In recent weeks the pro-Russian rebels have suffered a series of heavy defeats, losing large chunks of territory, with their empire shrivelled to the two major eastern cities of Donetsk and Luhansk. On Wednesday, rebels ambushed a bus carrying nationalist fighters, killing 12. The insurgents also captured an unknown number of the fighters from Right Sector, extreme nationalists who are supporting government forces.

As Ukraine has warned of a major buildup of Russian forces on its border Putin's intentions have remained opaque. Russian state television showed footage of men in beige T-shirts and caps loading water and baby food on to the trucks. These reports stated the convoy contained 2,000 tonnes of aid, including grain, sugar, medicine, sleeping bags and power generators.

Some believed the convoy was a made-for-television propaganda stunt to help the largely Russian-speaking population of eastern Ukraine. Others were convinced the slow-moving column was a classic "Trojan horse" intelligence operation to smuggle weapons to rebel militias rapidly running low on fuel and ammunition.

International aid officials admit that Russia's ostensibly humanitarian operation is particularly sensitive given the backdrop of what Ukraine claims is an undercover "hybrid" war waged by Moscow on Ukrainian territory.

On Tuesday, the French president, François Hollande, told Putin in a phone call that he had "grave concerns" about Russia's ongoing unilateral mission in Ukraine.

Ukraine’s interim Prime Minister Arseniy Yatsenyuk said Russian convoy would not cross the border. Photograph: Andrew Kravchenko/AP

The US secretary of state, John Kerry, said Putin's attendance at the G20 summit in Brisbane in November depended on how he responds to the Ukraine crisis in coming weeks.

Speaking in Australia, Kerry said no decision had yet been taken but added that the US understood Australia's "deep anger and need for justice" over the shooting down last month of Malaysia Airlines flight MH17, in which 298 people were killed – including 38 Australians. "This is an unconscionable crime of a huge international order," Kerry declared.

While a full investigation had yet to be completed, Kerry said there was no doubt about the type of weapon used and where it had come from.

"We saw the takeoff, we saw the hit, we saw this airplane disappear from the radar screen, so there is really no mystery," he said. "But we need to have the complete investigation to legitimise whatever steps are going to be taken as we go down the road."

The Russian military has been involved in preparing the convoy, which departed from Alabino, a town outside Moscow where the 2nd Guards Tamanskaya Motor Rifle Division is based. A YouTube video uploaded on 10 August showed soldiers standing next to the convoy and a missile launcher parked across the road. The video later disappeared.

An independent defence analyst, Anton Lavrov, said the video had indeed been taken at the Alabino military base, that some of the vehicles were obviously military trucks repainted white, and identified the launcher as Russia's powerful S-300 surface-to-air missile.

"I think it is a humanitarian PR ploy. If Russia can deliver aid it will raise its prestige, and the residents of eastern Ukraine will know it's Ukraine's fault they weren't getting humanitarian aid," Lavrov said. "If it does try to go through a rebel-controlled border crossing then it will be clear that this is not first and foremost humanitarian aid."

The Russian blogosphere was full of theories that the convoy was meant to provoke an attack so Russian troops could be deployed to protect it, or to begin a regular flow of Russian trucks into eastern Ukraine.

"This specific convoy could be clean. Because for now there's no need to bring weapons in some intricate manner – whole tank columns, Grad rockets, Gvozdika howitzers, Buk missiles are entering Ukraine without difficulty," the popular blogger and commentator Vladimir Golyshev wrote on Facebook.

"But tomorrow problems could arise with this. And for that reason it's important to set a precedent. This is a real diplomatic war."

The Russian nationalist website Sputnik & Pogrom argued that the convoy puts Kiev in a bind: accepting the aid would "completely destroy their narrative of a war with bloodthirsty Russians", but turning it away during a humanitarian crisis would also look bad. "One thing is for sure: the conflict that will develop around the convoy in the next few days will become yet another step toward the deployment of troops to Ukraine and the mobilisation of Russian public opinion for that deployment," the website wrote.

Andrei Illarionov, a former economic policy adviser to Putin who is now a fellow at the conservative Cato Institute in Washington, told the Ukrainian publication Gordon on Monday that any humanitarian convoy to Ukraine would be a sign of Russian aggression aimed at supporting the separatist cause.

"The deployment of a so called 'humanitarian convoy', 'peace-keeping forces', 'emergencies ministry units' is one of the steps of the methodology developed by the Russian authorities to seize foreign territories," he said.

Illarionov said Russia's emergencies ministry had conducted a similar humanitarian mission to Georgia in 1993. Georgian commentators later accused the operation of delivering arms to separatists in the Abkhazia region, which is now an unrecognised state propped up by Russia.