Multiple explosions could be heard late on Saturday and early on Sunday in the centre of the separatist-controlled city of Donetsk in eastern Ukraine, a Reuters reporter said.
The origin of the explosions was not clear. There was no immediate comment from separatist authorities or from Kyiv.
A diplomatic source told Reuters that the Organization for Security and Cooperation in Europe (OSCE) had recorded about 2,000 ceasefire violations between Ukrainian forces and the eastern autonomous region on Saturday, indicating an unprecedented rise in tensions.
Some security sources reported that two soldiers were killed and four others were wounded in heavy shelling in eastern Ukraine.
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