Kyiv — Ukraine is implementing "enhanced security measures in the northern regions" near its border with Belarus as Russia holds joint nuclear drills with its close ally, for which Moscow says "nuclear munitions were delivered" to field storage facilities.

Kyiv announced the heightened security posture along its northern border Thursday after warning for weeks of a possible fresh attack coming from Belarus, Russia's chief regional ally.

Kyiv has sounded the alarm that Russia may use Belarus — which it used as a springboard to launch its ongoing, full-scale invasion of Ukraine in February 2022 — to stage a new offensive from the north, including toward the capital Kyiv.

Ukraine's Security Service (SBU) said its units and the army were "carrying out a comprehensive set of enhanced security measures in the northern regions of our country."

The measures — including stepped up checks and controls of individuals and properties — "will serve as an effective deterrent to any aggressive actions or operations by the enemy and its ally," the SBU said in a statement.

The Kremlin on Monday dismissed Ukrainian allegations that it wanted to drag Belarus further into the war as "an attempt at further incitement."

But on Thursday, Russia's Defense Ministry said in a statement that, "as part of the nuclear forces exercise" taking place with Belarus, "nuclear munitions were delivered to the field storage facilities of the [Russian] missile brigade's position" in the country.

A video posted Thursday on social media by Belarus' Ministry of Defense, which appeared to have been created by the Russian Defense Ministry, showed a truck driving through a forest and unloading an item said to be related to the nuclear munitions.

Russia's military said the missile brigade in Belarus was carrying out training to receive munitions for mobile Iskander-M tactical missile launch systems, including exercises in loading munitions onto launch vehicles and moving them clandestinely in preparation for a hypothetical launch.

Speaking Wednesday, NATO Secretary General Mark Rutte said the alliance was monitoring the Russian-Belorussian exercises and warned that it's reaction to any Russian nuclear attack would be "devastating," according to the Kyiv Independent. 

There has been little significant change in the trajectory of the war, now well into its fifth year, in recent months, though Ukrainian forces — taking advantage of drone warfare technology — have, according to multiple reports, managed to at least slow the rate of Russia's encroachment.

A Wall Street Journal report published this week argued that Ukraine had in fact "wrestled Russia's much-larger army almost to a halt in recent months, having gained a tactical and technological edge," but it cautioned that it was too soon to declare the war had reached "a strategic turning point."