What are kamikaze drones? Here’s how Russia and Ukraine are using them.

Russia struck deep into Ukraine to strike the capital, Kyiv, with kamikaze drones — small airborne devices that can hit a target at a distance and are nimble enough to avoid many air defenses.

Here's what we know about the deadly aircraft and their role in the war.

The drones that Russia has been deploying, Ukrainian and U.S. officials say, are manufactured in Iran, where they are known as Shahed-136s. They are designed to strike specific targets with explosives that can be delivered at distances of up to 1,500 miles.

» READ MORE: Waves of explosive-laden drones strike Ukraine’s capital, killing four people

Russia has renamed the Shahed-136 as the Geran-2. Iran denies giving Russia drones for use in its war against Ukraine.

The drones are part of a category of weapon known as loitering munitions - meaning that they "are designed to loiter over battlefields," looking for targets such as radars, Ingvild Bode, an associate professor at the Center for War Studies, a research group within the University of Southern Denmark, previously told The Washington Post. "When they have found the target, [they] launch themselves onto it." That's why the "kamikaze" term is often applied to this and weapons such as U.S.-made Switchblade drones.

Because of the distinctive buzzing sounds they make as they approach, the Shahed-136s are typically less destructive than precision missiles - civilians can see and hear them coming, so they have more time to seek shelter before any explosion. And unlike large missiles, their blast radius is smaller and doesn't necessarily send shrapnel flying in every direction.

But they can also slip past Ukraine's air defenses - or force the military to use its limited air defense resources to neutralize them before they can strike their target.

Russian forces seeking an advantage on the battlefield have increasingly been making use of drones. U.S. and allied officials, speaking on the condition of anonymity to discuss security matters, have told The Post that Iran recently began delivering the drones and other weapons to Russia, sending technical advisers to train Russian forces in how to operate them. Pentagon officials have publicly confirmed the use of Iranian drones in Russian airstrikes.

Ukraine believes Russia has ordered as many as 2,400 kamikaze drones from Iran. In response, Kyiv has urged its allies to send sophisticated air defense systems.

Russia has largely used kamikaze drones to attack military and infrastructure targets in southern Ukraine. Its forces first deployed the Shahed-136 in northeastern Ukraine in September, according to Britain's Defense Ministry. In an intelligence update, the ministry argued that the use of the weapons near the front lines suggested "that Russia is attempting to use the system to conduct tactical strikes rather than against more strategic targets farther into Ukrainian territory."

Since mid-September, Ukrainian forces have claimed they shot down Iranian-made drones in various parts of Ukraine. Speaking by video conference to Group of Seven leaders last week, Ukrainian President Volodymyr Zelensky said, "Every 10 minutes I receive a message about the enemy's use of Iranian Shaheds."

This has led Kyiv to downgrade its diplomatic relations with Tehran. Zelensky called the partnership between Russia and Iran "collaboration with evil," while Tehran accused Kyiv of overreacting based on "unconfirmed reports" and "media hype by foreign parties."

The drones were used for the first time to strike central Kyiv on Monday in what appeared to be an attempt to target a thermal power station that supplies the capital. At least four people were killed in the blasts, officials said. Mykhailo Podolyak, a senior adviser to Zelensky, accused Iran of being "responsible for the murders of Ukrainians."

The United States has pledged to send Ukraine over 700 of its own kamikaze drones, called Switchblades, and trained some Ukrainian soldiers in April on how to use them.

With its thin body and ruler-shaped wings, the Switchblade drone is different in appearance from the Shahed-136, which looks like a miniature fighter plane. But the idea behind the two weapons is the same: Allow a remote operator to take out a target with deadly efficiency and evade detection and air defense.

Ukraine has also deployed Turkish-made Bayraktar TB2 drones and claims to have destroyed many Russian military targets with them. That drone is so popular in Ukraine that a Ukrainian soldier released a song in its honor.

Separately, the Guardian newspaper reported that two Ukrainians raised $9.6 million last week for the purchase of Ukrainian RAM II drones, which can carry an explosive payload of more than 6-pounds.