On the other side of this border in northern Ukraine, not visible through the thick pine and birch forests that crowd the E-95 highway but noticeable to passing truckers, a force is gathering in Belarus more potent than anything seen in the country since the fall of the Soviet Union, officials and military analysts say.

Russia has deployed tanks and artillery, fighter jets and helicopters, advanced rocket systems and troops by the thousands all across Belarus, augmenting a fighting force that will soon envelope Ukraine like a horseshoe on three sides. Russia says the troops have deployed for military exercises scheduled to commence next month, but the buildup in Belarus could presage an attack from a new vector, one in proximity to Ukraine’s capital, Kyiv.

With much of Ukraine’s military might concentrated in the country’s east — where a war with Russian-backed separatists has raged for eight years — military analysts and Ukraine’s own generals say it will be difficult for the country to muster the forces necessary to defend its northern border.