Ukraine has said it destroyed two bridges inside Russia by using a couple of cheap drones to hit stashes of mines and ammunition hidden there by Russian forces.

The Ukrainian military said the two bridges near the border with Ukraine’s Kharkiv region were being used by the Russian military to resupply their troops.

Because of their strategic importance, the bridges were mined – so that the Russian military had the option of blowing them up in case of a sudden Ukrainian advance.

It is not unusual for an army under attack to destroy bridges, roads and other key infrastructure on its own territory to prevent the enemy from advancing.

Ukraine did this in the early days of the full-scale invasion in February 2022, destroying bridges on roads leading towards Kyiv. The move delayed the Russian advance and protected the Ukrainian capital.

In the case of the two bridges in Russia, the Ukrainian military found out about the stashes of mines and used it to its own advantage.

Ukraine’s 58th Separate Motorised Infantry Brigade, which conducted the operation, told CNN that they decided have a closer look at the bridge after noticing unusual activity around it.

“It became clear that something was going on there.

We couldn’t fly a regular reconnaissance drone under the bridge because the signal would simply disappear, so we flew in with a first-person-view drone equipped with fibre optics,” a representative of the brigade told CNN.

A video filmed by the drone shows it approaching the bridge and discovering a large pile of anti-tank mines and other ammunition. A piece of fabric that appears to have been covering the stash is seen lying to the side.

“We saw the mines, and we struck,” they added.

The video ends abruptly when the drone hits the stash. Footage filmed by a second camera from some distance shows a large explosion.

CNN has geolocated the bridge seen in the video to the Belgorod region in southern Russia, near the border with Ukraine.

“After that, we decided to check the other bridge. We found it was also mined and we struck,” the brigade representative said, adding: “(We) saw an opportunity and took it.”

The bridges’ destruction – and the daring way Ukraine achieved it – is a rare piece of good news for Kyiv.

Ukraine is facing a tough situation along the frontlines as Russian troops continue to inch forward as Russian President Vladimir Putin continues to delay any ceasefire talks.

At the same time, Moscow keeps terrorising Ukraine’s civilian population with near-daily deadly aerial attacks against cities across the country.

Russia did not comment on the attacks against the bridges.

Cheap drones prove their value

The drones used in the attack costs between 25,000 and 30,000 Ukrainian hryvnas, or between $600 to $725, the brigade representative told CNN.

That makes the two attacks extremely cost-effective.

Taking down a bridge from afar is not an easy undertaking. Under normal circumstances, it would require expensive guided munitions delivered by a sophisticated system such as a missile launcher or plane.

Ukraine has previously said it used the Western-supplied High Mobility Artillery Rocket System (HIMARS) to blow up bridges in Russia’s Kursk region.

These are pricey weapons – when Germany purchased three HIMARS launchers for Ukraine from the United States last year, it paid $30 million in total.

Each missile costs tens of thousands of dollars.

But the bridge attacks were not the first time that Ukraine used small and relatively cheap first-person-view drones for maximum effect.

In June, Ukrainian forces destroyed or damaged dozens of Russian aircraft using small drones that were smuggled to the vicinity of Russian military airfields in trucks.