BERLIN - Russia and Ukraine's foreign ministers agreed in Berlin on Wednesday that new ceasefire talks should be held this week, as government forces battled pro-Moscow insurgents in the ex-Soviet state.
German Foreign Minister Frank-Walter Steinmeier had hastily convened the crisis meeting, also involving his French counterpart Laurent Fabius, warning that unless truce talks resume, the country could face "an explosion of violence".
Ukrainian troops backed by tanks and bomber jets have this week again fought separatist insurgents in the country's east, in Europe's worst fighting in nearly two decades that has claimed over 450 lives in 11 weeks.
The latest clashes came after Ukraine's President Petro Poroshenko 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.
In their joint statement, the four top envoys agreed that fresh talks should start by Saturday, July 5 at the latest involving Moscow, Kiev, the rebels and the Organisation for Security and Cooperation in Europe (OSCE).
The goal would be "reaching an unconditional and mutually agreed sustainable ceasefire", they said, also calling for the release of hostages, the protection of journalists and full Ukrainian control of its border checkpoints with Russia.
"An explosion of violence can occur at any time that can't be controlled politically or militarily," warned Steinmeier.
Amid the diplomatic efforts in Berlin, violence raged in Ukraine.
A spokesman for the national security and defence council in Kiev said militias had killed four Ukrainian soldiers and wounded 10 others in separate mortar fire attacks along the Russian border.
They were the first casualties reported by Kiev in the second stage of the low-scale war. Regional officials also confirmed the deaths of four civilians in a roadside attack on their bus.
Ukraine's acting Defence Minister Mykhailo Koval however told reporters that the military operation was progressing "according to plan. The advantage is on our side."
Ukrainian border guards and troops with armoured personnel carriers were in control of the Dolzhansky border post which they said they retook from the rebels on Tuesday.