While a diplomatic push sought to defuse the rhetoric, deadly shelling pummelled besieged pro-Russian rebel strongholds and a top separatist leader claimed he had received a fresh injection of troops trained "on Russian territory."
Moscow and Kiev's foreign ministers geared up for an urgent meeting with their French and German counterparts tomorrow as Ukraine's claim that it had destroyed a small military convoy from Russia ramped up the stakes.
European heads of state also tried to douse the flames with Ukrainian President Petro Poroshenko holding phone talks with German Chancellor Angela Merkel and meeting Finnish counterpart Sauli Niinistoe, who jetted to Kiev following a face-to-face with Russian leader Vladimir Putin on Friday.
French President Francois Hollande called for Ukraine to show "restraint and good judgement" as it pushed on to oust insurgents after four months of fighting that has killed over 2,100 people and left the region facing a humanitarian disaster.
More From This Section
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.
The International Committee of the Red Cross, which is overseeing the aid delivery, said today that an agreement was reached on checking the cargo but that "security guarantees" were still needed on how the lorries could cross rebel-held territory.
While Russia has denied funnelling weapons to the rebels, a top separatist leader claimed that troop reinforcements trained across the border had arrived to prop up the ailing insurgency.