Ukraine's border service said that nine guards were wounded when rebels shelled the Dolzhansky border post with Russia, a strategic crossing that Kiev won back days earlier in a step hailed as the "first victory" since the renewal of its military offencive.
Elsewhere, the defence ministry said in a statement that its forces had destroyed five trucks carrying "terrorists".
The statement said that rebels had launched 16 attacks on government checkpoints during the past 24 hours.
Ukraine's President Petro Poroshenko this week ripped up a 10-day truce, which Kiev says the insurgents broke over 100 times at the cost of 30 lives. The military then announced a "massive" anti-rebel operation in the eastern rustbelt.
They urged him to persuade the pro-Moscow separatists to negotiate.
Russia and Ukraine's foreign ministers agreeing in Berlin yesterday that the new talks for a fresh ceasefire should be held this week.
German Foreign Minister Frank-Walter Steinmeier hastily convened a crisis meeting, also involving his French counterpart Laurent Fabius, warning that unless truce talks resume, the country could face "an explosion of violence".
Both Kiev and the separatists refuse to negotiate directly with each other but the four envoys called for fresh talks by Saturday involving Moscow, a Kiev proxy, the rebels and the Organisation for Security and Cooperation in Europe (OSCE).
Rebels said today they were prepared to take part in indirect talks only if Moscow and international observers were involved.
"If Russia and the OSCE make a proposal to us then we are willing to participate in consultations," Andriy Purgin, deputy prime minister of the self-proclaimed Donetsk People's Republic, told AFP.