Ukraine has accused Russia of using suicide drones against civilian targets in Kiev.
They are believed to include Iran’s Shahed-136 drones, which Russia has been using since mid-September.
What is a Russian kamikaze drone?
The Shahed-136, which Russia calls Geranium-2, is a type of flying bomb.
It has a warhead packed with explosives and is designed to hover over a target until ordered to attack.
The explosives detonate on impact, destroying the drone in the process.
The Shahed-136 has a wingspan of about 2.5 m (8.2 ft) and can be difficult to detect by radar.
“They fly low and you can send them in waves. These swarms of drones are much more difficult for air defenses to deal with,” military expert Justin Crump told the BBC.
The Shahed-136 is also relatively cheap, at around $20,000 (£17,800).
It’s unclear exactly how many Russia has, but the US has said Iran plans to send hundreds to Russia. Iran has denied doing so.
Has Ukraine used kamikaze drones?
There have been recent attacks on a Russian military base in Saky, western Crimea, an air base near Sevastopol and Russian ships in the port of Sevastopol.
Dr Marina Miron, a defense studies researcher at King’s College London, says: ‘If you look at the bursts of attacks, they are quite small.
“I suspect that they are domestic suicide drones, with explosives attached.”
What other drones do Ukraine and Russia have?
Ukraine’s main military drone is Turkey’s Bayraktar TB2. It’s the size of a small plane, has cameras on board and can be armed with laser-guided bombs.
At the start of the war, Ukraine had a fleet of “fewer than 50” of them, says Dr Jack Watling of the Royal United Services Institute (RUSI) think-tank.
Russia also uses the “smaller, more basic” Orlan-10, which has cameras and can carry small bombs.
How have military drones been used?
For both sides – Russia and Ukraine – drones have been effective in finding enemy targets and directing artillery fire at them.
“Russian forces can bring weapons to bear on the enemy within three to five minutes of an Orlan-10 drone sighting a target,” says Dr Watling. An attack can otherwise take 20-30 minutes to complete.
Dr. Marina Miron says drones allow Ukraine to stretch limited forces.
“In the past if you wanted to scout enemy positions, you would have to send in special forces units … and you might lose some troops,” he says. “Now, all you’re risking is a drone.”
In the first weeks of the war, Ukraine’s Bayraktar drones were widely praised.
However, many Bayraktars were destroyed by Russian air defense systems, as they were large and slow.
How are non-military drones used?
Military drones are expensive to replace – a single Bayraktar TB2 costs around $2m (£1.7m).
So both sides – but especially Ukraine – also use small, commercial models, such as the DJI Mavic 3, which costs around £1,700.
These commercial drones can be equipped with small bombs. However, they are mainly used to detect enemy troops and direct attacks.
“Ukraine doesn’t have as much ammunition as Russia,” says Dr. Miron. “Having ‘eyes in the sky’ to spot targets and direct artillery fire means they can make better use of what they have.”
But commercial drones are much more powerful than military ones.
The total flying distance of the DJI Mavic is only 30 km, and it can fly for a maximum of 46 minutes.
Cheaper and smaller drones fly for even less time and cover shorter distances.
How does each side defend against drones?
Russia uses radar defenses against military drones, and electronic devices against commerce, says Dr. Miron.
“The Russian forces have the Stupor rifle, which fires electromagnetic pulses,” he says. This prevents commercial drones from being able to navigate using GPS, he explained.
These systems can cause a drone to crash or return to base, and stop returning information.