BRUSSELS

 The European Commission warned Thursday of the possibility of a new cycle of violence in the conflict opposing pro-Russian separatists and Ukrainian forces in the country's eastern regions. 

European Commission spokeswoman Maja Kocijancic told reporters in Brussels on Thursday: "This renewed intensive fighting is likely to create a new spiral of violence and suffering."

 "The [Minsk] cease-fire agreement needs to be respected and all heavy fires withdrawn," she said, calling Wednesday's clashes, which, according to Ukrainian security officials, near Donetsk the "most serious violation" under the EU-brokered Minsk cease-fire agreement reached between Russia and the 28-nation bloc in February. 

The Feb. 12 Minsk cease-fire agreement, which includes among other stipulations the withdrawal of heavy weaponry and of all foreign armed formations from combat areas, has failed to be implemented fully, with daily reports of breaches and clashes. Both parties blame each other for violating the accord.

Meanwhile, the Organization for Security and Co-operation (OSCE) in Europe has reported sightings of Russian soldiers in eastern Ukraine late May to Anadolu Agency on Thursday.

"Soldiers in Russian uniforms and vehicles with Russian number plates have been seen by our Special Monitoring Mission [SMM]," said Iryna Gudyma, senior press assistant of the OSCE Special Monitoring Mission to Ukraine, on Thursday.

She gave an example of an incident dated May 28 from the organization's records.

"In Petrovske [pro-Russian separatist-controlled territory 38 kilometers southeast of Donetsk] the [Special Monitoring Mission] spoke to a young man who said that the former local holiday camp was currently occupied by an unknown armed group. He could not specify for how long this armed group had been stationed in the village. In the village, the [Mission] spoke to two women, both wearing military uniforms, with caps with Russian Federation Armed Forces insignia," the report provided by Gudyma said

Then two women in a vehicle with Russian Federation number plates stopped next to the OSCE vehicles, the report said.

"Two armed men, also in Russian Federation uniforms, exited the car and ordered the women to stop the conversation with the [Special Monitoring Mission]. Behind a tall fence inside the holiday camp, the SMM observed one infantry fighting vehicle," the report said.

This is not the first Russian troop sighting that has been reported in eastern Ukraine. 

On May 20, the OSCE said two Russian servicemen captured by Ukrainian forces in the eastern Donbass region had claimed to be "members of a unit of the Armed Forces of the Russian Federation".

Russia has continued to deny that the country's armed forces are engaged in the fighting in Ukraine.

More than 6,000 people have lost their lives in the conflict between Ukrainian forces and pro-Russian separatists since April 2014, according to the UN.