The European Union warned on Thursday that a flare-up in fighting in eastern Ukraine could create a "new spiral" of violence and recalled that EU leaders have said they could tighten sanctions on Russia.
The warning came as Ukraine's ambassador to the EU, Kostiantyn Yelisieiev, urged the bloc to take immediate steps to ramp up sanctions on Moscow over the renewed fighting.
Calling clashes on Wednesday near Donetsk the worst violation since an EU-brokered ceasefire took effect in February, a spokeswoman for the EU's executive Commission told a news briefing: "This renewed intensive fighting is likely to create a new spiral of violence and suffering."
The EU spokesperson called on all sides to respect the Minsk ceasefire agreement and recalled that EU leaders in March had linked future decisions on easing or tightening their sanctions against Moscow to implementation of that deal.
"The leaders have made a very clear link between the restrictive measures and the full implementation of Minsk, but they have also said that they remain if necessary (ready to) take further steps," she said. "This remains the EU's position."
Yelisieiev said the Minsk agreements were on the brink of complete breakdown and said what Kiev says was a separatist attack on the eastern town of Maryinka should trigger stronger EU economic sanctions against Moscow.
In a statement, the ambassador urged the EU "to take immediate steps to support the territorial integrity and sovereignty of Ukraine, in particular by ramping up the sanctions pressure on Moscow."
Ukrainian President Petro Poroshenko also warned of an escalation of violence in an address to the nation's parliament on Thursday, telling lawmakers that there were 9,000 Russian servicemen on Ukrainian territory and warned of the threat of a "full-scale invasion" by Russia along the whole joint border.
"The military must be ready as much for a renewal of an offensive by the enemy in the Donbass as they are for a full-scale invasion along the whole length of the border with Russia. We must be truly ready for this," Poroshenko said.
"The Ukrainian side has taken steps to aggravate tensions many times in the past in the run up to some major international events. This used to happen and we are seriously concerned now over the most recent manifestation of such activity," Kremlin spokesman Dmitry Peskov told journalists.
Russia, for its part accused Kiev of provoking the renewed fighting in east Ukraine to put pressure on the European Union to keep sanctions in place.
EU leaders agreed in March that economic sanctions on Russia would stay in place until the Minsk agreement is fully implemented, effectively extending them to the end of the year.
A formal decision to renew the EU sanctions on Russia's financial, energy and defence sectors is expected to be taken when the leaders next meet on June 25 and 26.