London CNN  — 

Ukrainian drone strikes taking place inside Russia once seemed an unthinkable prospect. But such attacks have become an increasingly common feature of Moscow’s war – with an emboldened Kyiv warning that more will come.

A string of drone strikes have peppered Russian cities including Moscow throughout the summer. Friday saw one of the most dramatic yet – sea drones targeted a major Russian port hundreds of miles from Ukrainian-held territory, leaving a warship listing.

They have distracted from a Ukrainian counteroffensive that is yet to produce tangible results on the battlefield, and brought the war home to Russia.

But they are not without risk for Kyiv, which is attempting to seize the front foot in the war while maintaining relations with Western nations wary of any hint of escalation.

Here’s what you need to know.

A series of strikes

Ukrainian President Volodymyr Zelensky warned last week that war is “gradually returning” to Russia, after the latest in a series of drone attacks to take place inside the country that Moscow has pinned on Kyiv.

Last weekend’s incidents saw buildings in Moscow targeted by drones. On Tuesday, a drone struck the same skyscraper in Moscow that was hit on Sunday.

It followed two similar attempted attacks that were reported by Russian officials earlier in July, and numerous such incidents in June. In May, an apparent drone attack above the Kremlin led to dramatic images of blasts in the skies above the seat of Russian power.

A damaged building in Moscow following last weekend's drone strikes.

Ukraine has typically not taken direct responsibility for the attacks, though its responses have become more bullish in recent weeks. “The distance and deniability between Kyiv and these attacks is significantly less,” Douglas Barrie, a senior fellow for Military Aerospace at the International Institute for Strategic Studies (IISS), told CNN. “There now seems to be almost a tacit recognition that it was (them).”

Ukrainian Minister Mykhailo Fedorov, whose Digital Transformation Ministry oversees the country’s “Army of Drones” procurement plan, had said there would be more drone strikes to come as Kyiv ramps up its parallel summer counteroffensive aimed at pushing Russian troops out of Ukrainian territory.

Limited but effective weapon systems

It is difficult to establish exactly which weapons systems are being used in the attacks, and precisely which buildings are being targeted, with both the Russian and Ukrainian sides refusing to be drawn on the details of the incidents.

But there are clearly vast differences between these attacks, which are limited in scope, have caused few casualties and have not been aimed towards residential buildings, with those that Moscow has launched indiscriminately at Ukrainian population centers.

“Whether or not they’re actually arriving on their intended targets, the targets do seem to be buildings that are linked with the prosecution of the war in Ukraine,” Keir Giles, a Russia expert at Chatham House and the author of books on Russia’s invasion and foreign policy, told CNN. “In that respect, it’s a very different approach to what we’ve seen in Russia, with indiscriminate terror attacks.”

Giles notes there is “an open question of exactly how Ukraine is doing the attacks.” But the strikes have “shown up the incapacity of Russia’s defenses,” he added.

The one-way unmanned aerial vehicles (UAVs) that have seemingly been launched “carry a pretty small warhead and they’ve been used in small numbers, so in terms of direct military affect, it’s limited to put it mildly,” said Barrie.

“The kinds of systems that Ukraine is using are simple, comparatively speaking, but for their purpose they’re effective,” Barrie added.

Crucially, there is no suggestion that the weapons have been donated by the West. “These are systems (Ukraine) can manufacture themselves,” Barrie said, allowing Kyiv to send military messages to the Russian people alongside its defensive war at home, which NATO nations have been supporting with military aid.