by Anais LLOBET with Maria ANTONOVA in Kiev

KAMENSK-SHAKHTINSKY (AFP) – Diplomatic efforts to douse an international firestorm over claims that Ukraine’s forces destroyed Russian military vehicles ratcheted up Saturday as Moscow demanded that Kiev allow its mammoth aid convoy to cross the volatile border.

Moscow and Kiev’s foreign ministers prepared for an urgent meeting with their French and German counterparts Sunday after the United States blasted Russia for its “extremely dangerous” escalation of the crisis in Ukraine.

French President Francois Hollande meanwhile urged Ukraine to show “restraint and good judgement” as it pushed on with a brutal offensive to oust insurgents after four months of fighting that has killed over 2,000 people and left the region facing a humanitarian disaster.

The latest spike in tensions came after Ukrainian President Petro Poroshenko claimed his troops had blown up part of a small Russian military convoy that British media spotted breaching the porous frontier on Thursday.

Russia dismissed the claims as “fantasies”, its latest denial of persistent allegations from the West that it is arming the rebels.

– Aid ‘still waiting’ –

Amid the international slanging match, some 280 trucks packed with what Russia claims is humanitarian aid waited for a third day some 30 kilometres (20 miles) from a rebel-held border post as Moscow and Kiev haggled over letting it across.

The West and Kiev fear the convoy could be a “Trojan horse” to bolster the flagging pro-Kremlin rebellion in eastern Ukraine or provide Moscow with an excuse to send in the 20,000 troops that NATO says it has amassed on the border.

Russia’s foreign ministry has repeatedly demanded in recent days that Kiev cease fire in order for the aid to reach residents of blighted cities in the east who have been stuck for days without water or power.

AFP correspondents at the border heard blasts from the Ukrainian side and saw Moscow’s military hardware rumble along Russian territory close to the frontier.

Ukraine says it has sent scores of border officials to the Russian side to scour aid cargo but insists they are waiting for permission from the Red Cross to start work.

A spokeswoman for the International Committee of the Red Cross — which is meant to be overseeing the operation — told AFP that so far no inspections have started as negotiations continue.

“There was a meeting this morning between the Ukrainians and the Russians. We did not participate,” said Galina Balzamova. “We are still waiting for agreement” between them, she added.

– Rebel reinforcements –

While Russia has denied all claims it is funnelling weapons to the rebels, a top separatist leader claimed that reinforcements trained across the border had arrived to prop up the ailing insurgency.

A fresh injection of firepower consisted of 150 pieces of hardware and 1,200 personnel “who have received four months of training on Russian territory,” Alexander Zakharchenko, prime minister of the self-proclaimed Donetsk People’s Republic, said in a video posted on a rebel website.

“They have been brought in at the most crucial moment,” he said.

In Donetsk, the largest rebel bastion, the rumble of shelling could be heard Saturday as government troops tightened the vice around separatist fighters holed up there.

AFP journalists found several houses aflame in Makiyivka, a city adjoining Donetsk, and saw large craters around a residential neighbourhood near a base of rebel special forces.

Human Rights Watch quoted residents fleeing Lugansk — the rebels second largest stronghold that has seen some of the worst fighting — as saying that the city was cut off from electricity, gas, and cell phone coverage, and that it was difficult to find drinking water and food.

The United Nations says over 285,000 people have fled the fighting in the east.

Ukraine’s security spokesman Andriy Lysenko said Saturday that three soldiers died and 13 were wounded in the past 24 hours.

President Poroshenko meanwhile wrote on Twitter that the army has taken over Zhdanivka, a town about 45 kilometres northeast of Donetsk.

– New hopes for talks –

A flurry of diplomacy to calm tensions saw Ukraine, Russia, France and Germany agree to get their top diplomats together for a meeting in Berlin on Sunday.

Germany’s Frank-Walter Steinmeier told Bild newspaper that he hoped the talks would help “put an end to violent fighting” in eastern Ukraine and provide the territories with “urgent and necessary aid”.

Ukraine’s Foreign Minister Pavlo Klimkin said the sides “need to talk”.

The French presidency suggested that Sunday’s meeting could be a “first step” towards another face-to-face encounter between the heads of state.