Germany warned today that direct military clashes between Russia and Ukraine must be avoided at all costs as Kiev and Moscow's top diplomats joined crisis talks with only faint hope of a breakthrough.
The foreign ministers of Russia, Ukraine, Germany and France gathered in Berlin after Moscow again denied claims it had sent weapons across the border to prop up the flagging separatist rebellion.
German Foreign Minister Frank-Walter Steinmeier said ahead of the talks that all sides must be "very careful... about sliding ever deeper into a direct confrontation between Ukrainian and Russian armed forces".
"This must be avoided at all cost," said Steinmeier before meeting Ukraine's Foreign Minister Pavlo Klimkin, Russia's Sergei Lavrov and Laurent Fabius of France.
He cautioned that "there are no guarantees that today's talks will lead to the success we desire" but stressed that "it would be irresponsible ... Not to take advantage of this willingness to talk".
The question would be "whether there is a path toward a ceasefire that is realistic and resilient and that offers us hope of ending the violence," he said.
On the ground in east Ukraine, Kiev's military said it hoisted the national flag over a district police station in a northeast suburb of the second-largest rebel bastion of Lugansk after a fierce battle with pro-Russian separatists yesterday.
A push into the city limits of the stricken 420,000-strong industrial hub would be a major breakthrough for government forces after four months of fighting that has claimed more than 2,100 lives and brought the region to the brink of a humanitarian catastrophe.
Ukraine also ramped up the stakes before the talks in Germany by alleging another military convoy that included three Grad rocket systems crossed over from Russia.
The fresh claims come as a furore still swirls over Kiev's earlier boasts that it destroyed part of a Russian armoured convoy which breached the frontier Thursday.
Ukraine's Klimkin said today's talks with his Russian counterpart would "not be easy" as Germany also demanded that Moscow clarify rebel claims that they had received hundreds of fighters trained in Russia to shore up their insurgency.
A Kremlin spokesman denied Moscow had sent "equipment" across the border, its latest dismissal of persistent allegations by the West that it is arming the rebels.
Meanwhile, Russia and Ukraine continued to haggle over a mammoth Russian aid convoy parked near the border as officials said inspections of the roughly 300 lorries would not start today.