Deep in a pine forest in southern Russia, military trucks, their silhouettes blurred by camouflage netting, appear through the trees. Soldiers in four-wheel-drive vehicles creep along rutted dirt roads. And outside a newly pitched tent camp, sentries, Kalashnikovs slung over their shoulders, pace back and forth.

Over the past month or so, Russia has deployed what analysts are calling the largest military buildup along the border with Ukraine since the outset of Kyiv’s war with Russian-backed separatists seven years ago.

It is far from a clandestine operation: During a trip to southern Russia by a New York Times journalist, evidence of the buildup was everywhere to be seen.

The mobilization is setting off alarms in the North Atlantic Treaty Organization, European capitals and Washington, and is increasingly seen as an early foreign policy test for the Biden administration, which just hit Moscow with a new round of sanctions. Russia responded almost immediately, announcing on Friday that it would expel 10 U.S. diplomats.

Ukraine’s minister of defense, Andrii Taran, told European lawmakers on Wednesday that Russia is now garrisoning about 110,000 soldiers near the Ukrainian border. In Washington, the director of the C.I.A. told Congress that it remains unclear whether the buildup is a show of force or preparation for something more ominous.

Even if the goal of the buildup remains unclear, military analysts say it was most certainly meant to be seen. A show of force is hardly a good show if nobody watches.

“They are deploying in a very visible way,” said Michael Kofman, a senior researcher at CNA, a think tank based in Arlington, Va., who has been monitoring the military activity. “They are doing it overtly, so we can see it. It is intentional.”