Serhiy Haidai, head of the Luhansk regional military administration in eastern Ukraine, said Monday that the Russian military had been gathering a "significant accumulation of troops and military equipment" in the region, in apparent preparation for an offensive push.
"Yes, I can confirm, that there is a significant accumulation of troops and military equipment that is getting prepared for the major breakthrough [in Luhansk region]," he said, speaking on national television.
"There was an attempt of a breakthrough in Rubizhne this night, our defenders repelled an attack. We are holding out, but we do see there's a major accumulation of troops."
Leaders in the Russian-backed separatist Donetsk and Luhansk People's Republics previously announced a "full mobilization" in the territories under their control.
Haidai said the mobilization was underway, but added that the newly mobilized recruits were inexperienced and were "being used as cannon fodder."
The Russian military has said it is pulling back its forces from around Kyiv and the northern Ukrainian city of Chernihiv to concentrate efforts in the Donbas region of Ukraine's east.