Russian forces battling Ukraine's assault are discovering a nasty danger behind them, courtesy of the US

• Ukraine is firing an artillery shell that lays mines built to destroy tanks.
• The US has sent Ukraine over 10,000 of these rounds along with the 155 mm howitzers that fire them.

The Russian troops defending the front lines against Ukraine's advance are discovering a danger lurking behind them, and it's one that threatens to make their positions more precarious.

The danger comes from an artillery round being fired over their heads.

"THE ENEMY IS REMOTELY MINING OUR REAR, ROUTES OF SUPPLY OF AMMUNITION AND RESERVES," Alexander Sladkov, a prominent pro-Russian military blogger, wrote in a Thursday Telegram post.

Sladkov wrote that Ukrainian forces were firing the Remote Anti-Armor Mine System, a US-made artillery round that lays anti-tank mines in flight. The US has sent Ukraine more than 10,000 of these rounds along with the 155 mm howitzers that can fire them out to a range of nearly 11 miles.

The mine-laying artillery shell is designed to force desperate choices. Vehicles must run a gauntlet laid with mines to deliver fresh troops, ammunition, fuel, and food to front-line positions. It also can be used to set traps along escape routes for front-line forces.

The mines self-destruct at certain times depending on the variant — some in under 24 hours and some more than a day later. Sladkov said these munitions, which Ukraine was first observed using in December, could be countered or defeated.

"These mines self-destruct after 4 hours, the M73 variant - after 48 hours," he wrote. "Engineering reconnaissance (sappers checking routes) easily cope with them." Whether it's as easy as this pro-Russian voice argues is debatable because this community tends to downplay threats while overselling Russian capabilities.

The dangers for Russia are multiplying, and Ukraine's counteroffensive appears to be underway. Kyiv's forces are attacking Russia's positions with Western-made tanks, infantry fighting vehicles, artillery, and other weapon systems that could force them into a retreat along paths that might be mined.