Germany has warned of an “explosive” situation in eastern Ukraine after a weekend of heavy shelling between government troops and Russian-backed separatists.

Several Ukrainian soldiers and civilians were killed and injured in recent nights amid what Kiev, the rebels and international monitors have called the worst violence since a supposed ceasefire deal was agreed in Minsk, Belarus, in February.

“The situation in eastern Ukraine is explosive,” Berlin’s foreign minister Frank-Walter Steinmeier told a German newspaper on Sunday.

“There is a lot at stake. If both parties in the conflict don’t return to the peace process, a new spiral of military escalation could be triggered at any time.”

Denis Pushilin, a senior official in the rebels’ so-called Donetsk People’s Republic (DNR), urged the leaders of Ukraine, Russia, Germany and France to “intervene immediately, or the situation will lead to full-scale military action”.

“This level of shelling has not been seen in the DNR for a long time. It’s one of the clearest provocations from the Ukrainian armed forces in recent months,” he said on Sunday.

“Because of this, we found ourselves yesterday one step away from full-scale military action.”

Talks sought

Mr Pushilin said he would seek talks with monitors from the Organisation for Security and Co-operation in Europe (OSCE) to discuss the rising violence. Last weekend, four of the OSCE’s vehicles were set on fire and destroyed outside the hotel where they are based in Donetsk.

Kiev says it is being forced to respond to intensified artillery fire from the rebels, and both sides appear to be using howitzers, tanks and multiple-rocket systems that under the Minsk deal are supposed to be removed from the frontline.

As well as growing more intense, the shelling has spread to a number of key areas in Donetsk and Luhansk regions, which are partly held by the separatists.

The area around the ruins of Donetsk airport remains a hot spot, and the main road linking rebel-held Donetsk to the southern city of Mariupol – a strategic, government-controlled port on the Sea of Azov – is now a focus for fighting.

Ukrainian officials say the country’s troops are acting with restraint but are ready to respond with full force if rebel attacks continue to increase; they also claim that thousands of Russian troops are in eastern Ukraine and just over the border inside Russia, and appear to be at a high state of combat readiness.

Moscow denies involvement in Ukraine’s conflict, despite the death and capture of Russian servicemen in battle and the clear presence in the conflict zone of Russian military equipment, including high-tech missile, radar and communication systems.

Kiev and Moscow gave no immediate response to a suggestion from new Polish president Andrzej Duda to expand talks on Ukraine’s conflict to include “the strongest states in Europe and Ukraine’s neighbours, including Poland”.

The presence at talks of Poland – a strong ally of Ukraine – could help Kiev as it comes under pressure from Russia, Germany and France to make concessions to the rebels.